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/>.
40 #include "ucioption.h"
48 // Set to true to force running with one thread. Used for debugging
49 const bool FakeSplit = false;
51 // Different node types, used as template parameter
52 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
54 // RootMove struct is used for moves at the root of the tree. For each root
55 // move, we store a score, a node count, and a PV (really a refutation
56 // in the case of moves which fail low). Score is normally set at
57 // -VALUE_INFINITE for all non-pv moves.
60 // RootMove::operator<() is the comparison function used when
61 // sorting the moves. A move m1 is considered to be better
62 // than a move m2 if it has an higher score
63 bool operator<(const RootMove& m) const { return score < m.score; }
65 void extract_pv_from_tt(Position& pos);
66 void insert_pv_in_tt(Position& pos);
74 // RootMoveList struct is mainly a std::vector of RootMove objects
75 struct RootMoveList : public std::vector<RootMove> {
77 void init(Position& pos, Move searchMoves[]);
78 RootMove* find(const Move& m, int startIndex = 0);
86 // Lookup table to check if a Piece is a slider and its access function
87 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
88 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
92 // Maximum depth for razoring
93 const Depth RazorDepth = 4 * ONE_PLY;
95 // Dynamic razoring margin based on depth
96 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
98 // Maximum depth for use of dynamic threat detection when null move fails low
99 const Depth ThreatDepth = 5 * ONE_PLY;
101 // Step 9. Internal iterative deepening
103 // Minimum depth for use of internal iterative deepening
104 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
106 // At Non-PV nodes we do an internal iterative deepening search
107 // when the static evaluation is bigger then beta - IIDMargin.
108 const Value IIDMargin = Value(0x100);
110 // Step 11. Decide the new search depth
112 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
113 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
114 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
115 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
116 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
118 // Minimum depth for use of singular extension
119 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
121 // Step 12. Futility pruning
123 // Futility margin for quiescence search
124 const Value FutilityMarginQS = Value(0x80);
126 // Futility lookup tables (initialized at startup) and their access functions
127 Value FutilityMargins[16][64]; // [depth][moveNumber]
128 int FutilityMoveCounts[32]; // [depth]
130 inline Value futility_margin(Depth d, int mn) {
132 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
133 : 2 * VALUE_INFINITE;
136 inline int futility_move_count(Depth d) {
138 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
141 // Step 14. Reduced search
143 // Reduction lookup tables (initialized at startup) and their access function
144 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
146 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
148 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
151 // Easy move margin. An easy move candidate must be at least this much
152 // better than the second best move.
153 const Value EasyMoveMargin = Value(0x150);
156 /// Namespace variables
162 int MultiPV, UCIMultiPV, MultiPVIdx;
164 // Time management variables
165 volatile bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
169 // Skill level adjustment
171 bool SkillLevelEnabled;
179 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
181 template <NodeType NT>
182 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
184 template <NodeType NT>
185 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
187 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
188 bool connected_moves(const Position& pos, Move m1, Move m2);
189 Value value_to_tt(Value v, int ply);
190 Value value_from_tt(Value v, int ply);
191 bool can_return_tt(const TTEntry* tte, Depth depth, Value beta, int ply);
192 bool connected_threat(const Position& pos, Move m, Move threat);
193 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
194 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
195 void do_skill_level(Move* best, Move* ponder);
197 int elapsed_search_time(int set = 0);
198 string score_to_uci(Value v, Value alpha = -VALUE_INFINITE, Value beta = VALUE_INFINITE);
199 string speed_to_uci(int64_t nodes);
200 string pv_to_uci(const Move pv[], int pvNum, bool chess960);
201 string pretty_pv(Position& pos, int depth, Value score, int time, Move pv[]);
202 string depth_to_uci(Depth depth);
203 void wait_for_stop_or_ponderhit();
205 // MovePickerExt template class extends MovePicker and allows to choose at compile
206 // time the proper moves source according to the type of node. In the default case
207 // we simply create and use a standard MovePicker object.
208 template<bool SpNode> struct MovePickerExt : public MovePicker {
210 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
211 : MovePicker(p, ttm, d, h, ss, b) {}
214 // In case of a SpNode we use split point's shared MovePicker object as moves source
215 template<> struct MovePickerExt<true> : public MovePicker {
217 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
218 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
220 Move get_next_move() { return mp->get_next_move(); }
224 // Overload operator<<() to make it easier to print moves in a coordinate
225 // notation compatible with UCI protocol.
226 std::ostream& operator<<(std::ostream& os, Move m) {
228 bool chess960 = (os.iword(0) != 0); // See set960()
229 return os << move_to_uci(m, chess960);
232 // When formatting a move for std::cout we must know if we are in Chess960
233 // or not. To keep using the handy operator<<() on the move the trick is to
234 // embed this flag in the stream itself. Function-like named enum set960 is
235 // used as a custom manipulator and the stream internal general-purpose array,
236 // accessed through ios_base::iword(), is used to pass the flag to the move's
237 // operator<<() that will read it to properly format castling moves.
240 std::ostream& operator<< (std::ostream& os, const set960& f) {
242 os.iword(0) = int(f);
246 // extension() decides whether a move should be searched with normal depth,
247 // or with extended depth. Certain classes of moves (checking moves, in
248 // particular) are searched with bigger depth than ordinary moves and in
249 // any case are marked as 'dangerous'. Note that also if a move is not
250 // extended, as example because the corresponding UCI option is set to zero,
251 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
252 template <bool PvNode>
253 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
254 bool moveIsCheck, bool* dangerous) {
255 assert(m != MOVE_NONE);
257 Depth result = DEPTH_ZERO;
258 *dangerous = moveIsCheck;
260 if (moveIsCheck && pos.see_sign(m) >= 0)
261 result += CheckExtension[PvNode];
263 if (type_of(pos.piece_on(move_from(m))) == PAWN)
265 Color c = pos.side_to_move();
266 if (relative_rank(c, move_to(m)) == RANK_7)
268 result += PawnPushTo7thExtension[PvNode];
271 if (pos.pawn_is_passed(c, move_to(m)))
273 result += PassedPawnExtension[PvNode];
278 if ( captureOrPromotion
279 && type_of(pos.piece_on(move_to(m))) != PAWN
280 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
281 - PieceValueMidgame[pos.piece_on(move_to(m))] == VALUE_ZERO)
284 result += PawnEndgameExtension[PvNode];
288 return std::min(result, ONE_PLY);
294 /// init_search() is called during startup to initialize various lookup tables
298 int d; // depth (ONE_PLY == 2)
299 int hd; // half depth (ONE_PLY == 1)
302 // Init reductions array
303 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
305 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
306 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
307 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
308 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
311 // Init futility margins array
312 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
313 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
315 // Init futility move count array
316 for (d = 0; d < 32; d++)
317 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
321 /// perft() is our utility to verify move generation. All the leaf nodes up to
322 /// the given depth are generated and counted and the sum returned.
324 int64_t perft(Position& pos, Depth depth) {
329 // Generate all legal moves
330 MoveList<MV_LEGAL> ml(pos);
332 // If we are at the last ply we don't need to do and undo
333 // the moves, just to count them.
334 if (depth <= ONE_PLY)
337 // Loop through all legal moves
339 for ( ; !ml.end(); ++ml)
341 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
342 sum += perft(pos, depth - ONE_PLY);
343 pos.undo_move(ml.move());
349 /// think() is the external interface to Stockfish's search, and is called when
350 /// the program receives the UCI 'go' command. It initializes various global
351 /// variables, and calls id_loop(). It returns false when a "quit" command is
352 /// received during the search.
354 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
356 static Book book; // Defined static to initialize the PRNG only once
358 // Save "search start" time and reset elapsed time to zero
359 elapsed_search_time(get_system_time());
361 // Initialize global search-related variables
362 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = false;
365 // Set output stream mode: normal or chess960. Castling notation is different
366 cout << set960(pos.is_chess960());
368 // Look for a book move
369 if (Options["OwnBook"].value<bool>())
371 if (Options["Book File"].value<string>() != book.name())
372 book.open(Options["Book File"].value<string>());
374 Move bookMove = book.probe(pos, Options["Best Book Move"].value<bool>());
375 if (bookMove != MOVE_NONE)
378 wait_for_stop_or_ponderhit();
380 cout << "bestmove " << bookMove << endl;
385 // Read UCI options: GUI could change UCI parameters during the game
386 read_evaluation_uci_options(pos.side_to_move());
387 Threads.read_uci_options();
389 // Set a new TT size if changed
390 TT.set_size(Options["Hash"].value<int>());
392 if (Options["Clear Hash"].value<bool>())
394 Options["Clear Hash"].set_value("false");
398 UCIMultiPV = Options["MultiPV"].value<int>();
399 SkillLevel = Options["Skill Level"].value<int>();
401 // Do we have to play with skill handicap? In this case enable MultiPV that
402 // we will use behind the scenes to retrieve a set of possible moves.
403 SkillLevelEnabled = (SkillLevel < 20);
404 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, 4) : UCIMultiPV);
406 // Write current search header to log file
407 if (Options["Use Search Log"].value<bool>())
409 Log log(Options["Search Log Filename"].value<string>());
410 log << "\nSearching: " << pos.to_fen()
411 << "\ninfinite: " << Limits.infinite
412 << " ponder: " << Limits.ponder
413 << " time: " << Limits.time
414 << " increment: " << Limits.increment
415 << " moves to go: " << Limits.movesToGo
419 // Wake up needed threads and reset maxPly counter
420 for (int i = 0; i < Threads.size(); i++)
422 Threads[i].maxPly = 0;
423 Threads[i].wake_up();
426 // Set best timer interval to avoid lagging under time pressure. Timer is
427 // used to check for remaining available thinking time.
428 TimeMgr.init(Limits, pos.startpos_ply_counter());
430 if (TimeMgr.available_time())
431 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 8, 20)));
433 Threads.set_timer(100);
435 // Start async mode to catch UCI commands sent to us while searching,
436 // like "quit", "stop", etc.
437 Threads.start_listener();
439 // We're ready to start thinking. Call the iterative deepening loop function
440 Move ponderMove = MOVE_NONE;
441 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
443 // From now on any UCI command will be read in-sync with Threads.getline()
444 Threads.stop_listener();
446 // Stop timer, no need to check for available time any more
447 Threads.set_timer(0);
449 // This makes all the slave threads to go to sleep, if not already sleeping
452 // Write current search final statistics to log file
453 if (Options["Use Search Log"].value<bool>())
455 int e = elapsed_search_time();
457 Log log(Options["Search Log Filename"].value<string>());
458 log << "Nodes: " << pos.nodes_searched()
459 << "\nNodes/second: " << (e > 0 ? pos.nodes_searched() * 1000 / e : 0)
460 << "\nBest move: " << move_to_san(pos, bestMove);
463 pos.do_move(bestMove, st);
464 log << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
465 pos.undo_move(bestMove); // Return from think() with unchanged position
468 // When we reach max depth we arrive here even without a StopRequest, but if
469 // we are pondering or in infinite search, we shouldn't print the best move
470 // before we are told to do so.
471 if (!StopRequest && (Limits.ponder || Limits.infinite))
472 wait_for_stop_or_ponderhit();
474 // Could be MOVE_NONE when searching on a stalemate position
475 cout << "bestmove " << bestMove;
477 // UCI protol is not clear on allowing sending an empty ponder move, instead
478 // it is clear that ponder move is optional. So skip it if empty.
479 if (ponderMove != MOVE_NONE)
480 cout << " ponder " << ponderMove;
490 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
491 // with increasing depth until the allocated thinking time has been consumed,
492 // user stops the search, or the maximum search depth is reached.
494 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
496 SearchStack ss[PLY_MAX_PLUS_2];
497 Value bestValues[PLY_MAX_PLUS_2];
498 int bestMoveChanges[PLY_MAX_PLUS_2];
499 int depth, aspirationDelta;
500 Value bestValue, alpha, beta;
501 Move bestMove, skillBest, skillPonder;
502 bool bestMoveNeverChanged = true;
504 // Initialize stuff before a new search
505 memset(ss, 0, 4 * sizeof(SearchStack));
508 *ponderMove = bestMove = skillBest = skillPonder = MOVE_NONE;
509 depth = aspirationDelta = 0;
510 bestValue = alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
511 ss->currentMove = MOVE_NULL; // Hack to skip update gains
513 // Moves to search are verified and copied
514 Rml.init(pos, searchMoves);
516 // Handle special case of searching on a mate/stalemate position
519 cout << "info" << depth_to_uci(DEPTH_ZERO)
520 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
525 // Iterative deepening loop until requested to stop or target depth reached
526 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
528 // Save now last iteration's scores, before Rml moves are reordered
529 for (size_t i = 0; i < Rml.size(); i++)
530 Rml[i].prevScore = Rml[i].score;
532 Rml.bestMoveChanges = 0;
534 // MultiPV loop. We perform a full root search for each PV line
535 for (MultiPVIdx = 0; MultiPVIdx < std::min(MultiPV, (int)Rml.size()); MultiPVIdx++)
537 // Calculate dynamic aspiration window based on previous iterations
538 if (depth >= 5 && abs(Rml[MultiPVIdx].prevScore) < VALUE_KNOWN_WIN)
540 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
541 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
543 aspirationDelta = std::min(std::max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
544 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
546 alpha = std::max(Rml[MultiPVIdx].prevScore - aspirationDelta, -VALUE_INFINITE);
547 beta = std::min(Rml[MultiPVIdx].prevScore + aspirationDelta, VALUE_INFINITE);
551 alpha = -VALUE_INFINITE;
552 beta = VALUE_INFINITE;
555 // Start with a small aspiration window and, in case of fail high/low,
556 // research with bigger window until not failing high/low anymore.
558 // Search starts from ss+1 to allow referencing (ss-1). This is
559 // needed by update gains and ss copy when splitting at Root.
560 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
562 // Bring to front the best move. It is critical that sorting is
563 // done with a stable algorithm because all the values but the first
564 // and eventually the new best one are set to -VALUE_INFINITE and
565 // we want to keep the same order for all the moves but the new
566 // PV that goes to the front. Note that in case of MultiPV search
567 // the already searched PV lines are preserved.
568 sort<RootMove>(Rml.begin() + MultiPVIdx, Rml.end());
570 // In case we have found an exact score and we are going to leave
571 // the fail high/low loop then reorder the PV moves, otherwise
572 // leave the last PV move in its position so to be searched again.
573 // Of course this is needed only in MultiPV search.
574 if (MultiPVIdx && bestValue > alpha && bestValue < beta)
575 sort<RootMove>(Rml.begin(), Rml.begin() + MultiPVIdx);
577 // Write PV back to transposition table in case the relevant entries
578 // have been overwritten during the search.
579 for (int i = 0; i <= MultiPVIdx; i++)
580 Rml[i].insert_pv_in_tt(pos);
582 // If search has been stopped exit the aspiration window loop,
583 // note that sorting and writing PV back to TT is safe becuase
584 // Rml is still valid, although refers to the previous iteration.
588 // Send full PV info to GUI if we are going to leave the loop or
589 // if we have a fail high/low and we are deep in the search. UCI
590 // protocol requires to send all the PV lines also if are still
591 // to be searched and so refer to the previous search's score.
592 if ((bestValue > alpha && bestValue < beta) || elapsed_search_time() > 2000)
593 for (int i = 0; i < std::min(UCIMultiPV, (int)Rml.size()); i++)
595 bool updated = (i <= MultiPVIdx);
597 if (depth == 1 && !updated)
600 Depth d = (updated ? depth : depth - 1) * ONE_PLY;
601 Value s = (updated ? Rml[i].score : Rml[i].prevScore);
605 << (i == MultiPVIdx ? score_to_uci(s, alpha, beta) : score_to_uci(s))
606 << speed_to_uci(pos.nodes_searched())
607 << pv_to_uci(&Rml[i].pv[0], i + 1, pos.is_chess960())
611 // In case of failing high/low increase aspiration window and
612 // research, otherwise exit the fail high/low loop.
613 if (bestValue >= beta)
615 beta = std::min(beta + aspirationDelta, VALUE_INFINITE);
616 aspirationDelta += aspirationDelta / 2;
618 else if (bestValue <= alpha)
620 AspirationFailLow = true;
621 StopOnPonderhit = false;
623 alpha = std::max(alpha - aspirationDelta, -VALUE_INFINITE);
624 aspirationDelta += aspirationDelta / 2;
629 } while (abs(bestValue) < VALUE_KNOWN_WIN);
632 // Collect info about search result
633 bestMove = Rml[0].pv[0];
634 *ponderMove = Rml[0].pv[1];
635 bestValues[depth] = bestValue;
636 bestMoveChanges[depth] = Rml.bestMoveChanges;
638 // Skills: Do we need to pick now the best and the ponder moves ?
639 if (SkillLevelEnabled && depth == 1 + SkillLevel)
640 do_skill_level(&skillBest, &skillPonder);
642 if (Options["Use Search Log"].value<bool>())
644 Log log(Options["Search Log Filename"].value<string>());
645 log << pretty_pv(pos, depth, bestValue, elapsed_search_time(), &Rml[0].pv[0]) << endl;
648 // Filter out startup noise when monitoring best move stability
649 if (depth > 2 && bestMoveChanges[depth])
650 bestMoveNeverChanged = false;
652 // Do we have time for the next iteration? Can we stop searching now?
653 if (!StopRequest && !StopOnPonderhit && Limits.useTimeManagement())
655 // Take in account some extra time if the best move has changed
656 if (depth > 4 && depth < 50)
657 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
659 // Stop search if most of available time is already consumed. We probably don't
660 // have enough time to search the first move at the next iteration anyway.
661 if (elapsed_search_time() > (TimeMgr.available_time() * 62) / 100)
664 // Stop search early if one move seems to be much better than others
667 && ( bestMoveNeverChanged
668 || elapsed_search_time() > (TimeMgr.available_time() * 40) / 100))
670 Value rBeta = bestValue - EasyMoveMargin;
671 (ss+1)->excludedMove = bestMove;
672 (ss+1)->skipNullMove = true;
673 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth * ONE_PLY) / 2);
674 (ss+1)->skipNullMove = false;
675 (ss+1)->excludedMove = MOVE_NONE;
681 // If we are allowed to ponder do not stop the search now but keep pondering
682 if (StopRequest && Limits.ponder) // FIXME Limits.ponder is racy
685 StopOnPonderhit = true;
690 // When using skills overwrite best and ponder moves with the sub-optimal ones
691 if (SkillLevelEnabled)
693 if (skillBest == MOVE_NONE) // Still unassigned ?
694 do_skill_level(&skillBest, &skillPonder);
696 bestMove = skillBest;
697 *ponderMove = skillPonder;
704 // search<>() is the main search function for both PV and non-PV nodes and for
705 // normal and SplitPoint nodes. When called just after a split point the search
706 // is simpler because we have already probed the hash table, done a null move
707 // search, and searched the first move before splitting, we don't have to repeat
708 // all this work again. We also don't need to store anything to the hash table
709 // here: This is taken care of after we return from the split point.
711 template <NodeType NT>
712 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
714 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
715 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
716 const bool RootNode = (NT == Root || NT == SplitPointRoot);
718 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
719 assert(beta > alpha && beta <= VALUE_INFINITE);
720 assert(PvNode || alpha == beta - 1);
721 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
723 Move movesSearched[MAX_MOVES];
728 Move ttMove, move, excludedMove, threatMove;
731 Value bestValue, value, oldAlpha;
732 Value refinedValue, nullValue, futilityBase, futilityValue;
733 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
734 int moveCount = 0, playedMoveCount = 0;
735 Thread& thread = Threads[pos.thread()];
736 SplitPoint* sp = NULL;
738 refinedValue = bestValue = value = -VALUE_INFINITE;
740 inCheck = pos.in_check();
741 ss->ply = (ss-1)->ply + 1;
743 // Used to send selDepth info to GUI
744 if (PvNode && thread.maxPly < ss->ply)
745 thread.maxPly = ss->ply;
747 // Step 1. Initialize node
750 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
751 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
752 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
758 ttMove = excludedMove = MOVE_NONE;
759 threatMove = sp->threatMove;
760 goto split_point_start;
763 // Step 2. Check for aborted search and immediate draw
765 || pos.is_draw<false>()
766 || ss->ply > PLY_MAX) && !RootNode)
769 // Step 3. Mate distance pruning
772 alpha = std::max(value_mated_in(ss->ply), alpha);
773 beta = std::min(value_mate_in(ss->ply+1), beta);
778 // Step 4. Transposition table lookup
779 // We don't want the score of a partial search to overwrite a previous full search
780 // TT value, so we use a different position key in case of an excluded move.
781 excludedMove = ss->excludedMove;
782 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
783 tte = TT.probe(posKey);
784 ttMove = RootNode ? Rml[MultiPVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
786 // At PV nodes we check for exact scores, while at non-PV nodes we check for
787 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
788 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
789 // we should also update RootMoveList to avoid bogus output.
790 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
791 : can_return_tt(tte, depth, beta, ss->ply)))
794 ss->bestMove = move = ttMove; // Can be MOVE_NONE
795 value = value_from_tt(tte->value(), ss->ply);
799 && !pos.is_capture_or_promotion(move)
800 && move != ss->killers[0])
802 ss->killers[1] = ss->killers[0];
803 ss->killers[0] = move;
808 // Step 5. Evaluate the position statically and update parent's gain statistics
810 ss->eval = ss->evalMargin = VALUE_NONE;
813 assert(tte->static_value() != VALUE_NONE);
815 ss->eval = tte->static_value();
816 ss->evalMargin = tte->static_value_margin();
817 refinedValue = refine_eval(tte, ss->eval, ss->ply);
821 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
822 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
825 // Update gain for the parent non-capture move given the static position
826 // evaluation before and after the move.
827 if ( (move = (ss-1)->currentMove) != MOVE_NULL
828 && (ss-1)->eval != VALUE_NONE
829 && ss->eval != VALUE_NONE
830 && pos.captured_piece_type() == PIECE_TYPE_NONE
831 && !is_special(move))
833 Square to = move_to(move);
834 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
837 // Step 6. Razoring (is omitted in PV nodes)
839 && depth < RazorDepth
841 && refinedValue + razor_margin(depth) < beta
842 && ttMove == MOVE_NONE
843 && abs(beta) < VALUE_MATE_IN_PLY_MAX
844 && !pos.has_pawn_on_7th(pos.side_to_move()))
846 Value rbeta = beta - razor_margin(depth);
847 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
849 // Logically we should return (v + razor_margin(depth)), but
850 // surprisingly this did slightly weaker in tests.
854 // Step 7. Static null move pruning (is omitted in PV nodes)
855 // We're betting that the opponent doesn't have a move that will reduce
856 // the score by more than futility_margin(depth) if we do a null move.
859 && depth < RazorDepth
861 && refinedValue - futility_margin(depth, 0) >= beta
862 && abs(beta) < VALUE_MATE_IN_PLY_MAX
863 && pos.non_pawn_material(pos.side_to_move()))
864 return refinedValue - futility_margin(depth, 0);
866 // Step 8. Null move search with verification search (is omitted in PV nodes)
871 && refinedValue >= beta
872 && abs(beta) < VALUE_MATE_IN_PLY_MAX
873 && pos.non_pawn_material(pos.side_to_move()))
875 ss->currentMove = MOVE_NULL;
877 // Null move dynamic reduction based on depth
878 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
880 // Null move dynamic reduction based on value
881 if (refinedValue - PawnValueMidgame > beta)
884 pos.do_null_move<true>(st);
885 (ss+1)->skipNullMove = true;
886 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
887 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
888 (ss+1)->skipNullMove = false;
889 pos.do_null_move<false>(st);
891 if (nullValue >= beta)
893 // Do not return unproven mate scores
894 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
897 if (depth < 6 * ONE_PLY)
900 // Do verification search at high depths
901 ss->skipNullMove = true;
902 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
903 ss->skipNullMove = false;
910 // The null move failed low, which means that we may be faced with
911 // some kind of threat. If the previous move was reduced, check if
912 // the move that refuted the null move was somehow connected to the
913 // move which was reduced. If a connection is found, return a fail
914 // low score (which will cause the reduced move to fail high in the
915 // parent node, which will trigger a re-search with full depth).
916 threatMove = (ss+1)->bestMove;
918 if ( depth < ThreatDepth
920 && threatMove != MOVE_NONE
921 && connected_moves(pos, (ss-1)->currentMove, threatMove))
926 // Step 9. ProbCut (is omitted in PV nodes)
927 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
928 // and a reduced search returns a value much above beta, we can (almost) safely
929 // prune the previous move.
931 && depth >= RazorDepth + ONE_PLY
934 && excludedMove == MOVE_NONE
935 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
937 Value rbeta = beta + 200;
938 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
940 assert(rdepth >= ONE_PLY);
942 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
945 while ((move = mp.get_next_move()) != MOVE_NONE)
946 if (pos.pl_move_is_legal(move, ci.pinned))
948 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
949 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
956 // Step 10. Internal iterative deepening
957 if ( depth >= IIDDepth[PvNode]
958 && ttMove == MOVE_NONE
959 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
961 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
963 ss->skipNullMove = true;
964 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
965 ss->skipNullMove = false;
967 tte = TT.probe(posKey);
968 ttMove = tte ? tte->move() : MOVE_NONE;
971 split_point_start: // At split points actual search starts from here
973 // Initialize a MovePicker object for the current position
974 MovePickerExt<SpNode> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
976 ss->bestMove = MOVE_NONE;
977 futilityBase = ss->eval + ss->evalMargin;
978 singularExtensionNode = !RootNode
980 && depth >= SingularExtensionDepth[PvNode]
981 && ttMove != MOVE_NONE
982 && !excludedMove // Do not allow recursive singular extension search
983 && (tte->type() & VALUE_TYPE_LOWER)
984 && tte->depth() >= depth - 3 * ONE_PLY;
987 lock_grab(&(sp->lock));
988 bestValue = sp->bestValue;
991 // Step 11. Loop through moves
992 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
993 while ( bestValue < beta
994 && (move = mp.get_next_move()) != MOVE_NONE
995 && !thread.cutoff_occurred())
999 if (move == excludedMove)
1002 // At root obey the "searchmoves" option and skip moves not listed in Root
1003 // Move List, as a consequence any illegal move is also skipped. In MultiPV
1004 // mode we also skip PV moves which have been already searched.
1005 if (RootNode && !Rml.find(move, MultiPVIdx))
1008 // At PV and SpNode nodes we want all moves to be legal since the beginning
1009 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
1014 moveCount = ++sp->moveCount;
1015 lock_release(&(sp->lock));
1022 // This is used by time management
1023 FirstRootMove = (moveCount == 1);
1025 // Save the current node count before the move is searched
1026 nodes = pos.nodes_searched();
1028 // For long searches send current move info to GUI
1029 if (pos.thread() == 0 && elapsed_search_time() > 2000)
1030 cout << "info" << depth_to_uci(depth)
1031 << " currmove " << move
1032 << " currmovenumber " << moveCount + MultiPVIdx << endl;
1035 isPvMove = (PvNode && moveCount <= 1);
1036 givesCheck = pos.move_gives_check(move, ci);
1037 captureOrPromotion = pos.is_capture_or_promotion(move);
1039 // Step 12. Decide the new search depth
1040 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1042 // Singular extension search. If all moves but one fail low on a search of
1043 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1044 // is singular and should be extended. To verify this we do a reduced search
1045 // on all the other moves but the ttMove, if result is lower than ttValue minus
1046 // a margin then we extend ttMove.
1047 if ( singularExtensionNode
1049 && pos.pl_move_is_legal(move, ci.pinned)
1052 Value ttValue = value_from_tt(tte->value(), ss->ply);
1054 if (abs(ttValue) < VALUE_KNOWN_WIN)
1056 Value rBeta = ttValue - int(depth);
1057 ss->excludedMove = move;
1058 ss->skipNullMove = true;
1059 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1060 ss->skipNullMove = false;
1061 ss->excludedMove = MOVE_NONE;
1062 ss->bestMove = MOVE_NONE;
1068 // Update current move (this must be done after singular extension search)
1069 newDepth = depth - ONE_PLY + ext;
1071 // Step 13. Futility pruning (is omitted in PV nodes)
1073 && !captureOrPromotion
1077 && !is_castle(move))
1079 // Move count based pruning
1080 if ( moveCount >= futility_move_count(depth)
1081 && (!threatMove || !connected_threat(pos, move, threatMove))
1082 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1085 lock_grab(&(sp->lock));
1090 // Value based pruning
1091 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1092 // but fixing this made program slightly weaker.
1093 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1094 futilityValue = futilityBase + futility_margin(predictedDepth, moveCount)
1095 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1097 if (futilityValue < beta)
1101 lock_grab(&(sp->lock));
1102 if (futilityValue > sp->bestValue)
1103 sp->bestValue = bestValue = futilityValue;
1105 else if (futilityValue > bestValue)
1106 bestValue = futilityValue;
1111 // Prune moves with negative SEE at low depths
1112 if ( predictedDepth < 2 * ONE_PLY
1113 && bestValue > VALUE_MATED_IN_PLY_MAX
1114 && pos.see_sign(move) < 0)
1117 lock_grab(&(sp->lock));
1123 // Check for legality only before to do the move
1124 if (!pos.pl_move_is_legal(move, ci.pinned))
1130 ss->currentMove = move;
1131 if (!SpNode && !captureOrPromotion)
1132 movesSearched[playedMoveCount++] = move;
1134 // Step 14. Make the move
1135 pos.do_move(move, st, ci, givesCheck);
1137 // Step extra. pv search (only in PV nodes)
1138 // The first move in list is the expected PV
1140 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1141 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1144 // Step 15. Reduced depth search
1145 // If the move fails high will be re-searched at full depth.
1146 bool doFullDepthSearch = true;
1148 if ( depth > 3 * ONE_PLY
1149 && !captureOrPromotion
1152 && ss->killers[0] != move
1153 && ss->killers[1] != move
1154 && (ss->reduction = reduction<PvNode>(depth, moveCount)) != DEPTH_ZERO)
1156 Depth d = newDepth - ss->reduction;
1157 alpha = SpNode ? sp->alpha : alpha;
1159 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1160 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1162 ss->reduction = DEPTH_ZERO;
1163 doFullDepthSearch = (value > alpha);
1166 // Step 16. Full depth search
1167 if (doFullDepthSearch)
1169 alpha = SpNode ? sp->alpha : alpha;
1170 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1171 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1173 // Step extra. pv search (only in PV nodes)
1174 // Search only for possible new PV nodes, if instead value >= beta then
1175 // parent node fails low with value <= alpha and tries another move.
1176 if (PvNode && value > alpha && (RootNode || value < beta))
1177 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1178 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1182 // Step 17. Undo move
1183 pos.undo_move(move);
1185 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1187 // Step 18. Check for new best move
1190 lock_grab(&(sp->lock));
1191 bestValue = sp->bestValue;
1195 // Finished searching the move. If StopRequest is true, the search
1196 // was aborted because the user interrupted the search or because we
1197 // ran out of time. In this case, the return value of the search cannot
1198 // be trusted, and we don't update the best move and/or PV.
1199 if (RootNode && !StopRequest)
1201 // Remember searched nodes counts for this move
1202 RootMove* rm = Rml.find(move);
1203 rm->nodes += pos.nodes_searched() - nodes;
1205 // PV move or new best move ?
1206 if (isPvMove || value > alpha)
1210 rm->extract_pv_from_tt(pos);
1212 // We record how often the best move has been changed in each
1213 // iteration. This information is used for time management: When
1214 // the best move changes frequently, we allocate some more time.
1215 if (!isPvMove && MultiPV == 1)
1216 Rml.bestMoveChanges++;
1219 // All other moves but the PV are set to the lowest value, this
1220 // is not a problem when sorting becuase sort is stable and move
1221 // position in the list is preserved, just the PV is pushed up.
1222 rm->score = -VALUE_INFINITE;
1226 if (value > bestValue)
1229 ss->bestMove = move;
1233 && value < beta) // We want always alpha < beta
1236 if (SpNode && !thread.cutoff_occurred())
1238 sp->bestValue = value;
1239 sp->ss->bestMove = move;
1241 sp->is_betaCutoff = (value >= beta);
1245 // Step 19. Check for split
1247 && depth >= Threads.min_split_depth()
1249 && Threads.available_slave_exists(pos.thread())
1251 && !thread.cutoff_occurred())
1252 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, depth,
1253 threatMove, moveCount, &mp, NT);
1256 // Step 20. Check for mate and stalemate
1257 // All legal moves have been searched and if there are no legal moves, it
1258 // must be mate or stalemate. Note that we can have a false positive in
1259 // case of StopRequest or thread.cutoff_occurred() are set, but this is
1260 // harmless because return value is discarded anyhow in the parent nodes.
1261 // If we are in a singular extension search then return a fail low score.
1262 if (!SpNode && !moveCount)
1263 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1265 // Step 21. Update tables
1266 // If the search is not aborted, update the transposition table,
1267 // history counters, and killer moves.
1268 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1270 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1271 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1272 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1274 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1276 // Update killers and history only for non capture moves that fails high
1277 if ( bestValue >= beta
1278 && !pos.is_capture_or_promotion(move))
1280 if (move != ss->killers[0])
1282 ss->killers[1] = ss->killers[0];
1283 ss->killers[0] = move;
1285 update_history(pos, move, depth, movesSearched, playedMoveCount);
1291 // Here we have the lock still grabbed
1292 sp->is_slave[pos.thread()] = false;
1293 sp->nodes += pos.nodes_searched();
1294 lock_release(&(sp->lock));
1297 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1302 // qsearch() is the quiescence search function, which is called by the main
1303 // search function when the remaining depth is zero (or, to be more precise,
1304 // less than ONE_PLY).
1306 template <NodeType NT>
1307 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1309 const bool PvNode = (NT == PV);
1311 assert(NT == PV || NT == NonPV);
1312 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1313 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1314 assert(PvNode || alpha == beta - 1);
1316 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1320 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1321 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1325 Value oldAlpha = alpha;
1327 ss->bestMove = ss->currentMove = MOVE_NONE;
1328 ss->ply = (ss-1)->ply + 1;
1330 // Check for an instant draw or maximum ply reached
1331 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1334 // Decide whether or not to include checks, this fixes also the type of
1335 // TT entry depth that we are going to use. Note that in qsearch we use
1336 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1337 inCheck = pos.in_check();
1338 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1340 // Transposition table lookup. At PV nodes, we don't use the TT for
1341 // pruning, but only for move ordering.
1342 tte = TT.probe(pos.get_key());
1343 ttMove = (tte ? tte->move() : MOVE_NONE);
1345 if (!PvNode && tte && can_return_tt(tte, ttDepth, beta, ss->ply))
1347 ss->bestMove = ttMove; // Can be MOVE_NONE
1348 return value_from_tt(tte->value(), ss->ply);
1351 // Evaluate the position statically
1354 bestValue = futilityBase = -VALUE_INFINITE;
1355 ss->eval = evalMargin = VALUE_NONE;
1356 enoughMaterial = false;
1362 assert(tte->static_value() != VALUE_NONE);
1364 evalMargin = tte->static_value_margin();
1365 ss->eval = bestValue = tte->static_value();
1368 ss->eval = bestValue = evaluate(pos, evalMargin);
1370 // Stand pat. Return immediately if static value is at least beta
1371 if (bestValue >= beta)
1374 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1379 if (PvNode && bestValue > alpha)
1382 // Futility pruning parameters, not needed when in check
1383 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1384 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1387 // Initialize a MovePicker object for the current position, and prepare
1388 // to search the moves. Because the depth is <= 0 here, only captures,
1389 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1391 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1394 // Loop through the moves until no moves remain or a beta cutoff occurs
1395 while ( bestValue < beta
1396 && (move = mp.get_next_move()) != MOVE_NONE)
1398 assert(is_ok(move));
1400 givesCheck = pos.move_gives_check(move, ci);
1408 && !is_promotion(move)
1409 && !pos.is_passed_pawn_push(move))
1411 futilityValue = futilityBase
1412 + PieceValueEndgame[pos.piece_on(move_to(move))]
1413 + (is_enpassant(move) ? PawnValueEndgame : VALUE_ZERO);
1415 if (futilityValue < beta)
1417 if (futilityValue > bestValue)
1418 bestValue = futilityValue;
1423 // Prune moves with negative or equal SEE
1424 if ( futilityBase < beta
1425 && depth < DEPTH_ZERO
1426 && pos.see(move) <= 0)
1430 // Detect non-capture evasions that are candidate to be pruned
1431 evasionPrunable = !PvNode
1433 && bestValue > VALUE_MATED_IN_PLY_MAX
1434 && !pos.is_capture(move)
1435 && !pos.can_castle(pos.side_to_move());
1437 // Don't search moves with negative SEE values
1439 && (!inCheck || evasionPrunable)
1441 && !is_promotion(move)
1442 && pos.see_sign(move) < 0)
1445 // Don't search useless checks
1450 && !pos.is_capture_or_promotion(move)
1451 && ss->eval + PawnValueMidgame / 4 < beta
1452 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1454 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1455 bestValue = ss->eval + PawnValueMidgame / 4;
1460 // Check for legality only before to do the move
1461 if (!pos.pl_move_is_legal(move, ci.pinned))
1464 // Update current move
1465 ss->currentMove = move;
1467 // Make and search the move
1468 pos.do_move(move, st, ci, givesCheck);
1469 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1470 pos.undo_move(move);
1472 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1475 if (value > bestValue)
1478 ss->bestMove = move;
1482 && value < beta) // We want always alpha < beta
1487 // All legal moves have been searched. A special case: If we're in check
1488 // and no legal moves were found, it is checkmate.
1489 if (inCheck && bestValue == -VALUE_INFINITE)
1490 return value_mated_in(ss->ply);
1492 // Update transposition table
1493 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1494 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1495 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1497 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, move, ss->eval, evalMargin);
1499 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1505 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1506 // bestValue is updated only when returning false because in that case move
1509 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1511 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1512 Square from, to, ksq, victimSq;
1515 Value futilityValue, bv = *bestValue;
1517 from = move_from(move);
1519 them = flip(pos.side_to_move());
1520 ksq = pos.king_square(them);
1521 kingAtt = pos.attacks_from<KING>(ksq);
1522 pc = pos.piece_on(from);
1524 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1525 oldAtt = pos.attacks_from(pc, from, occ);
1526 newAtt = pos.attacks_from(pc, to, occ);
1528 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1529 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1531 if (!(b && (b & (b - 1))))
1534 // Rule 2. Queen contact check is very dangerous
1535 if ( type_of(pc) == QUEEN
1536 && bit_is_set(kingAtt, to))
1539 // Rule 3. Creating new double threats with checks
1540 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1544 victimSq = pop_1st_bit(&b);
1545 futilityValue = futilityBase + PieceValueEndgame[pos.piece_on(victimSq)];
1547 // Note that here we generate illegal "double move"!
1548 if ( futilityValue >= beta
1549 && pos.see_sign(make_move(from, victimSq)) >= 0)
1552 if (futilityValue > bv)
1556 // Update bestValue only if check is not dangerous (because we will prune the move)
1562 // connected_moves() tests whether two moves are 'connected' in the sense
1563 // that the first move somehow made the second move possible (for instance
1564 // if the moving piece is the same in both moves). The first move is assumed
1565 // to be the move that was made to reach the current position, while the
1566 // second move is assumed to be a move from the current position.
1568 bool connected_moves(const Position& pos, Move m1, Move m2) {
1570 Square f1, t1, f2, t2;
1577 // Case 1: The moving piece is the same in both moves
1583 // Case 2: The destination square for m2 was vacated by m1
1589 // Case 3: Moving through the vacated square
1590 p2 = pos.piece_on(f2);
1591 if ( piece_is_slider(p2)
1592 && bit_is_set(squares_between(f2, t2), f1))
1595 // Case 4: The destination square for m2 is defended by the moving piece in m1
1596 p1 = pos.piece_on(t1);
1597 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1600 // Case 5: Discovered check, checking piece is the piece moved in m1
1601 ksq = pos.king_square(pos.side_to_move());
1602 if ( piece_is_slider(p1)
1603 && bit_is_set(squares_between(t1, ksq), f2))
1605 Bitboard occ = pos.occupied_squares();
1606 clear_bit(&occ, f2);
1607 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
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) {
1651 assert(is_ok(threat));
1652 assert(!pos.is_capture_or_promotion(m));
1653 assert(!pos.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.is_capture(threat)
1669 && ( PieceValueMidgame[pos.piece_on(tfrom)] >= PieceValueMidgame[pos.piece_on(tto)]
1670 || type_of(pos.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 // can_return_tt() returns true if a transposition table score
1686 // can be used to cut-off at a given point in search.
1688 bool can_return_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 >= std::max(VALUE_MATE_IN_PLY_MAX, beta)
1694 || v < std::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 // current_search_time() returns the number of milliseconds which have passed
1740 // since the beginning of the current search.
1742 int elapsed_search_time(int set) {
1744 static int searchStartTime;
1747 searchStartTime = set;
1749 return get_system_time() - searchStartTime;
1753 // score_to_uci() converts a value to a string suitable for use with the UCI
1754 // protocol specifications:
1756 // cp <x> The score from the engine's point of view in centipawns.
1757 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1758 // use negative values for y.
1760 string score_to_uci(Value v, Value alpha, Value beta) {
1762 std::stringstream s;
1764 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1765 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1767 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1769 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1775 // speed_to_uci() returns a string with time stats of current search suitable
1776 // to be sent to UCI gui.
1778 string speed_to_uci(int64_t nodes) {
1780 std::stringstream s;
1781 int t = elapsed_search_time();
1783 s << " nodes " << nodes
1784 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1791 // pv_to_uci() returns a string with information on the current PV line
1792 // formatted according to UCI specification.
1794 string pv_to_uci(const Move pv[], int pvNum, bool chess960) {
1796 std::stringstream s;
1798 s << " multipv " << pvNum << " pv " << set960(chess960);
1800 for ( ; *pv != MOVE_NONE; pv++)
1807 // depth_to_uci() returns a string with information on the current depth and
1808 // seldepth formatted according to UCI specification.
1810 string depth_to_uci(Depth depth) {
1812 std::stringstream s;
1814 // Retrieve max searched depth among threads
1816 for (int i = 0; i < Threads.size(); i++)
1817 if (Threads[i].maxPly > selDepth)
1818 selDepth = Threads[i].maxPly;
1820 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1825 string time_to_string(int millisecs) {
1827 const int MSecMinute = 1000 * 60;
1828 const int MSecHour = 1000 * 60 * 60;
1830 int hours = millisecs / MSecHour;
1831 int minutes = (millisecs % MSecHour) / MSecMinute;
1832 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1834 std::stringstream s;
1839 s << std::setfill('0') << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
1843 string score_to_string(Value v) {
1845 std::stringstream s;
1847 if (v >= VALUE_MATE_IN_PLY_MAX)
1848 s << "#" << (VALUE_MATE - v + 1) / 2;
1849 else if (v <= VALUE_MATED_IN_PLY_MAX)
1850 s << "-#" << (VALUE_MATE + v) / 2;
1852 s << std::setprecision(2) << std::fixed << std::showpos << float(v) / PawnValueMidgame;
1858 // pretty_pv() creates a human-readable string from a position and a PV.
1859 // It is used to write search information to the log file (which is created
1860 // when the UCI parameter "Use Search Log" is "true").
1862 string pretty_pv(Position& pos, int depth, Value value, int time, Move pv[]) {
1864 const int64_t K = 1000;
1865 const int64_t M = 1000000;
1866 const int startColumn = 28;
1867 const size_t maxLength = 80 - startColumn;
1869 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1872 std::stringstream s;
1875 // First print depth, score, time and searched nodes...
1876 s << set960(pos.is_chess960())
1877 << std::setw(2) << depth
1878 << std::setw(8) << score_to_string(value)
1879 << std::setw(8) << time_to_string(time);
1881 if (pos.nodes_searched() < M)
1882 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1883 else if (pos.nodes_searched() < K * M)
1884 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1886 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1888 // ...then print the full PV line in short algebraic notation
1889 while (*m != MOVE_NONE)
1891 san = move_to_san(pos, *m);
1892 length += san.length() + 1;
1894 if (length > maxLength)
1896 length = san.length() + 1;
1897 s << "\n" + string(startColumn, ' ');
1901 pos.do_move(*m++, *st++);
1904 // Restore original position before to leave
1905 while (m != pv) pos.undo_move(*--m);
1911 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1912 // while the program is pondering. The point is to work around a wrinkle in
1913 // the UCI protocol: When pondering, the engine is not allowed to give a
1914 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1915 // We simply wait here until one of these commands (that raise StopRequest) is
1916 // sent, and return, after which the bestmove and pondermove will be printed.
1918 void wait_for_stop_or_ponderhit() {
1921 StopOnPonderhit = true;
1923 while (!StopRequest)
1925 Threads.getline(cmd);
1926 do_uci_async_cmd(cmd);
1931 // When playing with strength handicap choose best move among the MultiPV set
1932 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1934 void do_skill_level(Move* best, Move* ponder) {
1936 assert(MultiPV > 1);
1940 // Rml list is already sorted by score in descending order
1942 int max_s = -VALUE_INFINITE;
1943 int size = std::min(MultiPV, (int)Rml.size());
1944 int max = Rml[0].score;
1945 int var = std::min(max - Rml[size - 1].score, int(PawnValueMidgame));
1946 int wk = 120 - 2 * SkillLevel;
1948 // PRNG sequence should be non deterministic
1949 for (int i = abs(get_system_time() % 50); i > 0; i--)
1950 rk.rand<unsigned>();
1952 // Choose best move. For each move's score we add two terms both dependent
1953 // on wk, one deterministic and bigger for weaker moves, and one random,
1954 // then we choose the move with the resulting highest score.
1955 for (int i = 0; i < size; i++)
1959 // Don't allow crazy blunders even at very low skills
1960 if (i > 0 && Rml[i-1].score > s + EasyMoveMargin)
1963 // This is our magical formula
1964 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
1969 *best = Rml[i].pv[0];
1970 *ponder = Rml[i].pv[1];
1976 /// RootMove and RootMoveList method's definitions
1978 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1981 bestMoveChanges = 0;
1984 // Generate all legal moves and add them to RootMoveList
1985 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
1987 // If we have a searchMoves[] list then verify the move
1988 // is in the list before to add it.
1989 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
1991 if (sm != searchMoves && *sm != ml.move())
1995 rm.pv.push_back(ml.move());
1996 rm.pv.push_back(MOVE_NONE);
1997 rm.score = rm.prevScore = -VALUE_INFINITE;
2003 RootMove* RootMoveList::find(const Move& m, int startIndex) {
2005 for (size_t i = startIndex; i < size(); i++)
2006 if ((*this)[i].pv[0] == m)
2013 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2014 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2015 // allow to always have a ponder move even when we fail high at root and also a
2016 // long PV to print that is important for position analysis.
2018 void RootMove::extract_pv_from_tt(Position& pos) {
2020 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2025 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
2029 pos.do_move(m, *st++);
2031 while ( (tte = TT.probe(pos.get_key())) != NULL
2032 && tte->move() != MOVE_NONE
2033 && pos.is_pseudo_legal(tte->move())
2034 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
2036 && (!pos.is_draw<false>() || ply < 2))
2038 pv.push_back(tte->move());
2039 pos.do_move(tte->move(), *st++);
2042 pv.push_back(MOVE_NONE);
2044 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.is_pseudo_legal(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);
2082 // Thread::idle_loop() is where the thread is parked when it has no work to do.
2083 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint object
2084 // for which the thread is the master.
2086 void Thread::idle_loop(SplitPoint* sp) {
2090 // If we are not searching, wait for a condition to be signaled
2091 // instead of wasting CPU time polling for work.
2094 || (Threads.use_sleeping_threads() && !is_searching))
2096 assert((!sp && threadID) || Threads.use_sleeping_threads());
2098 // Slave thread should exit as soon as do_terminate flag raises
2105 // Grab the lock to avoid races with Thread::wake_up()
2106 lock_grab(&sleepLock);
2108 // If we are master and all slaves have finished don't go to sleep
2109 if (sp && Threads.split_point_finished(sp))
2111 lock_release(&sleepLock);
2115 // Do sleep after retesting sleep conditions under lock protection, in
2116 // particular we need to avoid a deadlock in case a master thread has,
2117 // in the meanwhile, allocated us and sent the wake_up() call before we
2118 // had the chance to grab the lock.
2119 if (do_sleep || !is_searching)
2120 cond_wait(&sleepCond, &sleepLock);
2122 lock_release(&sleepLock);
2125 // If this thread has been assigned work, launch a search
2128 assert(!do_terminate);
2130 // Copy split point position and search stack and call search()
2131 SearchStack ss[PLY_MAX_PLUS_2];
2132 SplitPoint* tsp = splitPoint;
2133 Position pos(*tsp->pos, threadID);
2135 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2138 if (tsp->nodeType == Root)
2139 search<SplitPointRoot>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2140 else if (tsp->nodeType == PV)
2141 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2142 else if (tsp->nodeType == NonPV)
2143 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2147 assert(is_searching);
2149 is_searching = false;
2151 // Wake up master thread so to allow it to return from the idle loop in
2152 // case we are the last slave of the split point.
2153 if ( Threads.use_sleeping_threads()
2154 && threadID != tsp->master
2155 && !Threads[tsp->master].is_searching)
2156 Threads[tsp->master].wake_up();
2159 // If this thread is the master of a split point and all slaves have
2160 // finished their work at this split point, return from the idle loop.
2161 if (sp && Threads.split_point_finished(sp))
2163 // Because sp->is_slave[] is reset under lock protection,
2164 // be sure sp->lock has been released before to return.
2165 lock_grab(&(sp->lock));
2166 lock_release(&(sp->lock));
2173 // do_uci_async_cmd() is called by listener thread when in async mode and 'cmd'
2174 // input line is received from the GUI.
2176 void do_uci_async_cmd(const std::string& cmd) {
2179 QuitRequest = StopRequest = true;
2181 else if (cmd == "stop")
2184 else if (cmd == "ponderhit")
2186 // The opponent has played the expected move. GUI sends "ponderhit" if
2187 // we were told to ponder on the same move the opponent has played. We
2188 // should continue searching but switching from pondering to normal search.
2189 Limits.ponder = false;
2191 if (StopOnPonderhit)
2197 // do_timer_event() is called by the timer thread when the timer triggers
2199 void do_timer_event() {
2201 static int lastInfoTime;
2202 int e = elapsed_search_time();
2204 // Print debug information every second
2205 if (get_system_time() - lastInfoTime >= 1000)
2207 lastInfoTime = get_system_time();
2210 dbg_print_hit_rate();
2213 // Should we stop the search?
2217 bool stillAtFirstMove = FirstRootMove
2218 && !AspirationFailLow
2219 && e > TimeMgr.available_time();
2221 bool noMoreTime = e > TimeMgr.maximum_time()
2222 || stillAtFirstMove;
2224 if ( (Limits.useTimeManagement() && noMoreTime)
2225 || (Limits.maxTime && e >= Limits.maxTime)
2226 /* missing nodes limit */ ) // FIXME