2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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/>.
37 #include "ucioption.h"
41 volatile SignalsType Signals;
43 std::vector<RootMove> RootMoves;
44 Position RootPosition;
52 using namespace Search;
54 // For some reason argument-dependent lookup (ADL) doesn't work for Android's
55 // STLPort, so explicitly qualify following functions.
61 // Set to true to force running with one thread. Used for debugging
62 const bool FakeSplit = false;
64 // Different node types, used as template parameter
65 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
67 // Lookup table to check if a Piece is a slider and its access function
68 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
69 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
71 // Maximum depth for razoring
72 const Depth RazorDepth = 4 * ONE_PLY;
74 // Dynamic razoring margin based on depth
75 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
77 // Maximum depth for use of dynamic threat detection when null move fails low
78 const Depth ThreatDepth = 5 * ONE_PLY;
80 // Minimum depth for use of internal iterative deepening
81 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
83 // At Non-PV nodes we do an internal iterative deepening search
84 // when the static evaluation is bigger then beta - IIDMargin.
85 const Value IIDMargin = Value(256);
87 // Minimum depth for use of singular extension
88 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
90 // Futility margin for quiescence search
91 const Value FutilityMarginQS = Value(128);
93 // Futility lookup tables (initialized at startup) and their access functions
94 Value FutilityMargins[16][64]; // [depth][moveNumber]
95 int FutilityMoveCounts[32]; // [depth]
97 inline Value futility_margin(Depth d, int mn) {
99 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
100 : 2 * VALUE_INFINITE;
103 inline int futility_move_count(Depth d) {
105 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
108 // Reduction lookup tables (initialized at startup) and their access function
109 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
111 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
113 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
116 // Easy move margin. An easy move candidate must be at least this much better
117 // than the second best move.
118 const Value EasyMoveMargin = Value(0x150);
120 // This is the minimum interval in msec between two check_time() calls
121 const int TimerResolution = 5;
124 size_t MultiPV, UCIMultiPV, PVIdx;
128 bool SkillLevelEnabled, Chess960;
132 template <NodeType NT>
133 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
135 template <NodeType NT>
136 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
138 void id_loop(Position& pos);
139 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta);
140 bool connected_moves(const Position& pos, Move m1, Move m2);
141 Value value_to_tt(Value v, int ply);
142 Value value_from_tt(Value v, int ply);
143 bool can_return_tt(const TTEntry* tte, Depth depth, Value ttValue, Value beta);
144 bool connected_threat(const Position& pos, Move m, Move threat);
145 Value refine_eval(const TTEntry* tte, Value ttValue, Value defaultEval);
146 Move do_skill_level();
147 string score_to_uci(Value v, Value alpha = -VALUE_INFINITE, Value beta = VALUE_INFINITE);
148 void pv_info_to_log(Position& pos, int depth, Value score, int time, Move pv[]);
149 void pv_info_to_uci(const Position& pos, int depth, Value alpha, Value beta);
151 // MovePickerExt class template extends MovePicker and allows to choose at
152 // compile time the proper moves source according to the type of node. In the
153 // default case we simply create and use a standard MovePicker object.
154 template<bool SpNode> struct MovePickerExt : public MovePicker {
156 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, Stack* ss, Value b)
157 : MovePicker(p, ttm, d, h, ss, b) {}
160 // In case of a SpNode we use split point's shared MovePicker object as moves source
161 template<> struct MovePickerExt<true> : public MovePicker {
163 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, Stack* ss, Value b)
164 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
166 Move next_move() { return mp->next_move(); }
170 // is_dangerous() checks whether a move belongs to some classes of known
171 // 'dangerous' moves so that we avoid to prune it.
172 FORCE_INLINE bool is_dangerous(const Position& pos, Move m, bool captureOrPromotion) {
174 // Test for a pawn pushed to 7th or a passed pawn move
175 if (type_of(pos.piece_moved(m)) == PAWN)
177 Color c = pos.side_to_move();
178 if ( relative_rank(c, to_sq(m)) == RANK_7
179 || pos.pawn_is_passed(c, to_sq(m)))
183 // Test for a capture that triggers a pawn endgame
184 if ( captureOrPromotion
185 && type_of(pos.piece_on(to_sq(m))) != PAWN
187 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
188 - PieceValueMidgame[pos.piece_on(to_sq(m))] == VALUE_ZERO))
197 /// Search::init() is called during startup to initialize various lookup tables
199 void Search::init() {
201 int d; // depth (ONE_PLY == 2)
202 int hd; // half depth (ONE_PLY == 1)
205 // Init reductions array
206 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
208 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
209 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
210 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
211 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
214 // Init futility margins array
215 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
216 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
218 // Init futility move count array
219 for (d = 0; d < 32; d++)
220 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
224 /// Search::perft() is our utility to verify move generation. All the leaf nodes
225 /// up to the given depth are generated and counted and the sum returned.
227 int64_t Search::perft(Position& pos, Depth depth) {
232 MoveList<MV_LEGAL> ml(pos);
234 // At the last ply just return the number of moves (leaf nodes)
235 if (depth == ONE_PLY)
239 for ( ; !ml.end(); ++ml)
241 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
242 cnt += perft(pos, depth - ONE_PLY);
243 pos.undo_move(ml.move());
249 /// Search::think() is the external interface to Stockfish's search, and is
250 /// called by the main thread when the program receives the UCI 'go' command. It
251 /// searches from RootPosition and at the end prints the "bestmove" to output.
253 void Search::think() {
255 static Book book; // Defined static to initialize the PRNG only once
257 Position& pos = RootPosition;
258 Chess960 = pos.is_chess960();
259 Eval::RootColor = pos.side_to_move();
260 TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
264 if (RootMoves.empty())
266 cout << "info depth 0 score "
267 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW) << endl;
269 RootMoves.push_back(MOVE_NONE);
273 if (Options["OwnBook"] && !Limits.infinite)
275 Move bookMove = book.probe(pos, Options["Book File"], Options["Best Book Move"]);
277 if (bookMove && count(RootMoves.begin(), RootMoves.end(), bookMove))
279 std::swap(RootMoves[0], *find(RootMoves.begin(), RootMoves.end(), bookMove));
284 UCIMultiPV = Options["MultiPV"];
285 SkillLevel = Options["Skill Level"];
287 // Do we have to play with skill handicap? In this case enable MultiPV that
288 // we will use behind the scenes to retrieve a set of possible moves.
289 SkillLevelEnabled = (SkillLevel < 20);
290 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, (size_t)4) : UCIMultiPV);
292 if (Options["Use Search Log"])
294 Log log(Options["Search Log Filename"]);
295 log << "\nSearching: " << pos.to_fen()
296 << "\ninfinite: " << Limits.infinite
297 << " ponder: " << Limits.ponder
298 << " time: " << Limits.time[pos.side_to_move()]
299 << " increment: " << Limits.inc[pos.side_to_move()]
300 << " moves to go: " << Limits.movestogo
306 // Set best timer interval to avoid lagging under time pressure. Timer is
307 // used to check for remaining available thinking time.
308 if (Limits.use_time_management())
309 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)));
311 Threads.set_timer(100);
313 // We're ready to start searching. Call the iterative deepening loop function
316 Threads.set_timer(0); // Stop timer
319 if (Options["Use Search Log"])
321 int e = SearchTime.elapsed();
323 Log log(Options["Search Log Filename"]);
324 log << "Nodes: " << pos.nodes_searched()
325 << "\nNodes/second: " << (e > 0 ? pos.nodes_searched() * 1000 / e : 0)
326 << "\nBest move: " << move_to_san(pos, RootMoves[0].pv[0]);
329 pos.do_move(RootMoves[0].pv[0], st);
330 log << "\nPonder move: " << move_to_san(pos, RootMoves[0].pv[1]) << endl;
331 pos.undo_move(RootMoves[0].pv[0]);
336 // When we reach max depth we arrive here even without Signals.stop is raised,
337 // but if we are pondering or in infinite search, we shouldn't print the best
338 // move before we are told to do so.
339 if (!Signals.stop && (Limits.ponder || Limits.infinite))
340 pos.this_thread()->wait_for_stop_or_ponderhit();
342 // Best move could be MOVE_NONE when searching on a stalemate position
343 cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
344 << " ponder " << move_to_uci(RootMoves[0].pv[1], Chess960) << endl;
350 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
351 // with increasing depth until the allocated thinking time has been consumed,
352 // user stops the search, or the maximum search depth is reached.
354 void id_loop(Position& pos) {
356 Stack ss[MAX_PLY_PLUS_2];
357 int depth, prevBestMoveChanges;
358 Value bestValue, alpha, beta, delta;
359 bool bestMoveNeverChanged = true;
360 Move skillBest = MOVE_NONE;
362 memset(ss, 0, 4 * sizeof(Stack));
363 depth = BestMoveChanges = 0;
364 bestValue = delta = -VALUE_INFINITE;
365 ss->currentMove = MOVE_NULL; // Hack to skip update gains
367 // Iterative deepening loop until requested to stop or target depth reached
368 while (!Signals.stop && ++depth <= MAX_PLY && (!Limits.depth || depth <= Limits.depth))
370 // Save last iteration's scores before first PV line is searched and all
371 // the move scores but the (new) PV are set to -VALUE_INFINITE.
372 for (size_t i = 0; i < RootMoves.size(); i++)
373 RootMoves[i].prevScore = RootMoves[i].score;
375 prevBestMoveChanges = BestMoveChanges;
378 // MultiPV loop. We perform a full root search for each PV line
379 for (PVIdx = 0; PVIdx < std::min(MultiPV, RootMoves.size()); PVIdx++)
381 // Set aspiration window default width
382 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
385 alpha = RootMoves[PVIdx].prevScore - delta;
386 beta = RootMoves[PVIdx].prevScore + delta;
390 alpha = -VALUE_INFINITE;
391 beta = VALUE_INFINITE;
394 // Start with a small aspiration window and, in case of fail high/low,
395 // research with bigger window until not failing high/low anymore.
397 // Search starts from ss+1 to allow referencing (ss-1). This is
398 // needed by update gains and ss copy when splitting at Root.
399 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
401 // Bring to front the best move. It is critical that sorting is
402 // done with a stable algorithm because all the values but the first
403 // and eventually the new best one are set to -VALUE_INFINITE and
404 // we want to keep the same order for all the moves but the new
405 // PV that goes to the front. Note that in case of MultiPV search
406 // the already searched PV lines are preserved.
407 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
409 // In case we have found an exact score and we are going to leave
410 // the fail high/low loop then reorder the PV moves, otherwise
411 // leave the last PV move in its position so to be searched again.
412 // Of course this is needed only in MultiPV search.
413 if (PVIdx && bestValue > alpha && bestValue < beta)
414 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
416 // Write PV back to transposition table in case the relevant
417 // entries have been overwritten during the search.
418 for (size_t i = 0; i <= PVIdx; i++)
419 RootMoves[i].insert_pv_in_tt(pos);
421 // If search has been stopped exit the aspiration window loop.
422 // Sorting and writing PV back to TT is safe becuase RootMoves
423 // is still valid, although refers to previous iteration.
427 // Send full PV info to GUI if we are going to leave the loop or
428 // if we have a fail high/low and we are deep in the search.
429 if ((bestValue > alpha && bestValue < beta) || SearchTime.elapsed() > 2000)
430 pv_info_to_uci(pos, depth, alpha, beta);
432 // In case of failing high/low increase aspiration window and
433 // research, otherwise exit the fail high/low loop.
434 if (bestValue >= beta)
439 else if (bestValue <= alpha)
441 Signals.failedLowAtRoot = true;
442 Signals.stopOnPonderhit = false;
450 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
452 } while (abs(bestValue) < VALUE_KNOWN_WIN);
455 // Skills: Do we need to pick now the best move ?
456 if (SkillLevelEnabled && depth == 1 + SkillLevel)
457 skillBest = do_skill_level();
459 if (!Signals.stop && Options["Use Search Log"])
460 pv_info_to_log(pos, depth, bestValue, SearchTime.elapsed(), &RootMoves[0].pv[0]);
462 // Filter out startup noise when monitoring best move stability
463 if (depth > 2 && BestMoveChanges)
464 bestMoveNeverChanged = false;
466 // Do we have time for the next iteration? Can we stop searching now?
467 if (!Signals.stop && !Signals.stopOnPonderhit && Limits.use_time_management())
469 bool stop = false; // Local variable, not the volatile Signals.stop
471 // Take in account some extra time if the best move has changed
472 if (depth > 4 && depth < 50)
473 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
475 // Stop search if most of available time is already consumed. We
476 // probably don't have enough time to search the first move at the
477 // next iteration anyway.
478 if (SearchTime.elapsed() > (TimeMgr.available_time() * 62) / 100)
481 // Stop search early if one move seems to be much better than others
484 && ( (bestMoveNeverChanged && pos.captured_piece_type())
485 || SearchTime.elapsed() > (TimeMgr.available_time() * 40) / 100))
487 Value rBeta = bestValue - EasyMoveMargin;
488 (ss+1)->excludedMove = RootMoves[0].pv[0];
489 (ss+1)->skipNullMove = true;
490 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
491 (ss+1)->skipNullMove = false;
492 (ss+1)->excludedMove = MOVE_NONE;
500 // If we are allowed to ponder do not stop the search now but
501 // keep pondering until GUI sends "ponderhit" or "stop".
503 Signals.stopOnPonderhit = true;
510 // When using skills swap best PV line with the sub-optimal one
511 if (SkillLevelEnabled)
513 if (skillBest == MOVE_NONE) // Still unassigned ?
514 skillBest = do_skill_level();
516 std::swap(RootMoves[0], *find(RootMoves.begin(), RootMoves.end(), skillBest));
521 // search<>() is the main search function for both PV and non-PV nodes and for
522 // normal and SplitPoint nodes. When called just after a split point the search
523 // is simpler because we have already probed the hash table, done a null move
524 // search, and searched the first move before splitting, we don't have to repeat
525 // all this work again. We also don't need to store anything to the hash table
526 // here: This is taken care of after we return from the split point.
528 template <NodeType NT>
529 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
531 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
532 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
533 const bool RootNode = (NT == Root || NT == SplitPointRoot);
535 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
536 assert((alpha == beta - 1) || PvNode);
537 assert(depth > DEPTH_ZERO);
539 Move movesSearched[64];
543 Move ttMove, move, excludedMove, bestMove, threatMove;
546 Value bestValue, value, oldAlpha, ttValue;
547 Value refinedValue, nullValue, futilityBase, futilityValue;
548 bool isPvMove, inCheck, singularExtensionNode, givesCheck;
549 bool captureOrPromotion, dangerous, doFullDepthSearch;
550 int moveCount = 0, playedMoveCount = 0;
551 Thread* thisThread = pos.this_thread();
552 SplitPoint* sp = NULL;
554 refinedValue = bestValue = value = -VALUE_INFINITE;
556 inCheck = pos.in_check();
557 ss->ply = (ss-1)->ply + 1;
559 // Used to send selDepth info to GUI
560 if (PvNode && thisThread->maxPly < ss->ply)
561 thisThread->maxPly = ss->ply;
563 // Step 1. Initialize node
567 ttMove = excludedMove = MOVE_NONE;
568 ttValue = VALUE_ZERO;
570 bestMove = sp->bestMove;
571 threatMove = sp->threatMove;
572 bestValue = sp->bestValue;
573 moveCount = sp->moveCount; // Lock must be held here
575 assert(bestValue > -VALUE_INFINITE && moveCount > 0);
577 goto split_point_start;
581 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
582 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
583 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
587 // Step 2. Check for aborted search and immediate draw
588 // Enforce node limit here. FIXME: This only works with 1 search thread.
589 if (Limits.nodes && pos.nodes_searched() >= Limits.nodes)
593 || pos.is_draw<false>()
594 || ss->ply > MAX_PLY) && !RootNode)
597 // Step 3. Mate distance pruning. Even if we mate at the next move our score
598 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
599 // a shorter mate was found upward in the tree then there is no need to search
600 // further, we will never beat current alpha. Same logic but with reversed signs
601 // applies also in the opposite condition of being mated instead of giving mate,
602 // in this case return a fail-high score.
605 alpha = std::max(mated_in(ss->ply), alpha);
606 beta = std::min(mate_in(ss->ply+1), beta);
611 // Step 4. Transposition table lookup
612 // We don't want the score of a partial search to overwrite a previous full search
613 // TT value, so we use a different position key in case of an excluded move.
614 excludedMove = ss->excludedMove;
615 posKey = excludedMove ? pos.exclusion_key() : pos.key();
616 tte = TT.probe(posKey);
617 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
618 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_ZERO;
620 // At PV nodes we check for exact scores, while at non-PV nodes we check for
621 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
622 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
623 // we should also update RootMoveList to avoid bogus output.
624 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == BOUND_EXACT
625 : can_return_tt(tte, depth, ttValue, beta)))
628 ss->currentMove = ttMove; // Can be MOVE_NONE
632 && !pos.is_capture_or_promotion(ttMove)
633 && ttMove != ss->killers[0])
635 ss->killers[1] = ss->killers[0];
636 ss->killers[0] = ttMove;
641 // Step 5. Evaluate the position statically and update parent's gain statistics
643 ss->eval = ss->evalMargin = VALUE_NONE;
646 assert(tte->static_value() != VALUE_NONE);
648 ss->eval = tte->static_value();
649 ss->evalMargin = tte->static_value_margin();
650 refinedValue = refine_eval(tte, ttValue, ss->eval);
654 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
655 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
658 // Update gain for the parent non-capture move given the static position
659 // evaluation before and after the move.
660 if ( (move = (ss-1)->currentMove) != MOVE_NULL
661 && (ss-1)->eval != VALUE_NONE
662 && ss->eval != VALUE_NONE
663 && !pos.captured_piece_type()
664 && !is_special(move))
666 Square to = to_sq(move);
667 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
670 // Step 6. Razoring (is omitted in PV nodes)
672 && depth < RazorDepth
674 && refinedValue + razor_margin(depth) < beta
675 && ttMove == MOVE_NONE
676 && abs(beta) < VALUE_MATE_IN_MAX_PLY
677 && !pos.pawn_on_7th(pos.side_to_move()))
679 Value rbeta = beta - razor_margin(depth);
680 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
682 // Logically we should return (v + razor_margin(depth)), but
683 // surprisingly this did slightly weaker in tests.
687 // Step 7. Static null move pruning (is omitted in PV nodes)
688 // We're betting that the opponent doesn't have a move that will reduce
689 // the score by more than futility_margin(depth) if we do a null move.
692 && depth < RazorDepth
694 && refinedValue - futility_margin(depth, 0) >= beta
695 && abs(beta) < VALUE_MATE_IN_MAX_PLY
696 && pos.non_pawn_material(pos.side_to_move()))
697 return refinedValue - futility_margin(depth, 0);
699 // Step 8. Null move search with verification search (is omitted in PV nodes)
704 && refinedValue >= beta
705 && abs(beta) < VALUE_MATE_IN_MAX_PLY
706 && pos.non_pawn_material(pos.side_to_move()))
708 ss->currentMove = MOVE_NULL;
710 // Null move dynamic reduction based on depth
711 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
713 // Null move dynamic reduction based on value
714 if (refinedValue - PawnValueMidgame > beta)
717 pos.do_null_move<true>(st);
718 (ss+1)->skipNullMove = true;
719 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
720 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
721 (ss+1)->skipNullMove = false;
722 pos.do_null_move<false>(st);
724 if (nullValue >= beta)
726 // Do not return unproven mate scores
727 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
730 if (depth < 6 * ONE_PLY)
733 // Do verification search at high depths
734 ss->skipNullMove = true;
735 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
736 ss->skipNullMove = false;
743 // The null move failed low, which means that we may be faced with
744 // some kind of threat. If the previous move was reduced, check if
745 // the move that refuted the null move was somehow connected to the
746 // move which was reduced. If a connection is found, return a fail
747 // low score (which will cause the reduced move to fail high in the
748 // parent node, which will trigger a re-search with full depth).
749 threatMove = (ss+1)->currentMove;
751 if ( depth < ThreatDepth
753 && threatMove != MOVE_NONE
754 && connected_moves(pos, (ss-1)->currentMove, threatMove))
759 // Step 9. ProbCut (is omitted in PV nodes)
760 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
761 // and a reduced search returns a value much above beta, we can (almost) safely
762 // prune the previous move.
764 && depth >= RazorDepth + ONE_PLY
767 && excludedMove == MOVE_NONE
768 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
770 Value rbeta = beta + 200;
771 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
773 assert(rdepth >= ONE_PLY);
774 assert((ss-1)->currentMove != MOVE_NONE);
775 assert((ss-1)->currentMove != MOVE_NULL);
777 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
780 while ((move = mp.next_move()) != MOVE_NONE)
781 if (pos.pl_move_is_legal(move, ci.pinned))
783 ss->currentMove = move;
784 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
785 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
792 // Step 10. Internal iterative deepening
793 if ( depth >= IIDDepth[PvNode]
794 && ttMove == MOVE_NONE
795 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
797 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
799 ss->skipNullMove = true;
800 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
801 ss->skipNullMove = false;
803 tte = TT.probe(posKey);
804 ttMove = tte ? tte->move() : MOVE_NONE;
807 split_point_start: // At split points actual search starts from here
809 MovePickerExt<SpNode> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
811 futilityBase = ss->eval + ss->evalMargin;
812 singularExtensionNode = !RootNode
814 && depth >= SingularExtensionDepth[PvNode]
815 && ttMove != MOVE_NONE
816 && !excludedMove // Recursive singular search is not allowed
817 && (tte->type() & BOUND_LOWER)
818 && tte->depth() >= depth - 3 * ONE_PLY;
820 // Step 11. Loop through moves
821 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
822 while ( bestValue < beta
823 && (move = mp.next_move()) != MOVE_NONE
824 && !thisThread->cutoff_occurred()
829 if (move == excludedMove)
832 // At root obey the "searchmoves" option and skip moves not listed in Root
833 // Move List, as a consequence any illegal move is also skipped. In MultiPV
834 // mode we also skip PV moves which have been already searched.
835 if (RootNode && !count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
838 // At PV and SpNode nodes we want all moves to be legal since the beginning
839 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
844 moveCount = ++sp->moveCount;
845 lock_release(sp->lock);
852 Signals.firstRootMove = (moveCount == 1);
854 if (thisThread == Threads.main_thread() && SearchTime.elapsed() > 2000)
855 cout << "info depth " << depth / ONE_PLY
856 << " currmove " << move_to_uci(move, Chess960)
857 << " currmovenumber " << moveCount + PVIdx << endl;
860 isPvMove = (PvNode && moveCount <= 1);
861 captureOrPromotion = pos.is_capture_or_promotion(move);
862 givesCheck = pos.move_gives_check(move, ci);
863 dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
866 // Step 12. Extend checks and, in PV nodes, also dangerous moves
867 if (PvNode && dangerous)
870 else if (givesCheck && pos.see_sign(move) >= 0)
873 // Singular extension search. If all moves but one fail low on a search of
874 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
875 // is singular and should be extended. To verify this we do a reduced search
876 // on all the other moves but the ttMove, if result is lower than ttValue minus
877 // a margin then we extend ttMove.
878 if ( singularExtensionNode
881 && pos.pl_move_is_legal(move, ci.pinned))
883 if (abs(ttValue) < VALUE_KNOWN_WIN)
885 Value rBeta = ttValue - int(depth);
886 ss->excludedMove = move;
887 ss->skipNullMove = true;
888 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
889 ss->skipNullMove = false;
890 ss->excludedMove = MOVE_NONE;
896 // Update current move (this must be done after singular extension search)
897 newDepth = depth - ONE_PLY + ext;
899 // Step 13. Futility pruning (is omitted in PV nodes)
901 && !captureOrPromotion
906 && (bestValue > VALUE_MATED_IN_MAX_PLY || bestValue == -VALUE_INFINITE))
908 // Move count based pruning
909 if ( moveCount >= futility_move_count(depth)
910 && (!threatMove || !connected_threat(pos, move, threatMove)))
918 // Value based pruning
919 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
920 // but fixing this made program slightly weaker.
921 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
922 futilityValue = futilityBase + futility_margin(predictedDepth, moveCount)
923 + H.gain(pos.piece_moved(move), to_sq(move));
925 if (futilityValue < beta)
933 // Prune moves with negative SEE at low depths
934 if ( predictedDepth < 2 * ONE_PLY
935 && pos.see_sign(move) < 0)
944 // Check for legality only before to do the move
945 if (!pos.pl_move_is_legal(move, ci.pinned))
951 ss->currentMove = move;
952 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
953 movesSearched[playedMoveCount++] = move;
955 // Step 14. Make the move
956 pos.do_move(move, st, ci, givesCheck);
958 // Step 15. Reduced depth search (LMR). If the move fails high will be
959 // re-searched at full depth.
960 if ( depth > 3 * ONE_PLY
962 && !captureOrPromotion
965 && ss->killers[0] != move
966 && ss->killers[1] != move)
968 ss->reduction = reduction<PvNode>(depth, moveCount);
969 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
970 alpha = SpNode ? sp->alpha : alpha;
972 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
974 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
975 ss->reduction = DEPTH_ZERO;
978 doFullDepthSearch = !isPvMove;
980 // Step 16. Full depth search, when LMR is skipped or fails high
981 if (doFullDepthSearch)
983 alpha = SpNode ? sp->alpha : alpha;
984 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
985 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
988 // Only for PV nodes do a full PV search on the first move or after a fail
989 // high, in the latter case search only if value < beta, otherwise let the
990 // parent node to fail low with value <= alpha and to try another move.
991 if (PvNode && (isPvMove || (value > alpha && (RootNode || value < beta))))
992 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
993 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
995 // Step 17. Undo move
998 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1000 // Step 18. Check for new best move
1003 lock_grab(sp->lock);
1004 bestValue = sp->bestValue;
1008 // Finished searching the move. If Signals.stop is true, the search
1009 // was aborted because the user interrupted the search or because we
1010 // ran out of time. In this case, the return value of the search cannot
1011 // be trusted, and we don't update the best move and/or PV.
1012 if (RootNode && !Signals.stop)
1014 RootMove& rm = *find(RootMoves.begin(), RootMoves.end(), move);
1016 // PV move or new best move ?
1017 if (isPvMove || value > alpha)
1020 rm.extract_pv_from_tt(pos);
1022 // We record how often the best move has been changed in each
1023 // iteration. This information is used for time management: When
1024 // the best move changes frequently, we allocate some more time.
1025 if (!isPvMove && MultiPV == 1)
1029 // All other moves but the PV are set to the lowest value, this
1030 // is not a problem when sorting becuase sort is stable and move
1031 // position in the list is preserved, just the PV is pushed up.
1032 rm.score = -VALUE_INFINITE;
1036 if (value > bestValue)
1043 && value < beta) // We want always alpha < beta
1046 if (SpNode && !thisThread->cutoff_occurred())
1048 sp->bestValue = value;
1049 sp->bestMove = move;
1057 // Step 19. Check for split
1059 && depth >= Threads.min_split_depth()
1060 && depth - reduction<PvNode>(depth, moveCount) >= Threads.min_split_depth()
1062 && Threads.available_slave_exists(thisThread)
1064 && !thisThread->cutoff_occurred())
1065 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
1066 depth, threatMove, moveCount, &mp, NT);
1069 // Step 20. Check for mate and stalemate
1070 // All legal moves have been searched and if there are no legal moves, it
1071 // must be mate or stalemate. Note that we can have a false positive in
1072 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1073 // harmless because return value is discarded anyhow in the parent nodes.
1074 // If we are in a singular extension search then return a fail low score.
1076 return excludedMove ? oldAlpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
1078 // If we have pruned all the moves without searching return a fail-low score
1079 if (bestValue == -VALUE_INFINITE)
1081 assert(!playedMoveCount);
1083 bestValue = oldAlpha;
1086 // Step 21. Update tables
1087 // Update transposition table entry, killers and history
1088 if (!SpNode && !Signals.stop && !thisThread->cutoff_occurred())
1090 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1091 bt = bestValue <= oldAlpha ? BOUND_UPPER
1092 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1094 TT.store(posKey, value_to_tt(bestValue, ss->ply), bt, depth, move, ss->eval, ss->evalMargin);
1096 // Update killers and history for non capture cut-off moves
1097 if ( bestValue >= beta
1098 && !pos.is_capture_or_promotion(move)
1101 if (move != ss->killers[0])
1103 ss->killers[1] = ss->killers[0];
1104 ss->killers[0] = move;
1107 // Increase history value of the cut-off move
1108 Value bonus = Value(int(depth) * int(depth));
1109 H.add(pos.piece_moved(move), to_sq(move), bonus);
1111 // Decrease history of all the other played non-capture moves
1112 for (int i = 0; i < playedMoveCount - 1; i++)
1114 Move m = movesSearched[i];
1115 H.add(pos.piece_moved(m), to_sq(m), -bonus);
1120 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1126 // qsearch() is the quiescence search function, which is called by the main
1127 // search function when the remaining depth is zero (or, to be more precise,
1128 // less than ONE_PLY).
1130 template <NodeType NT>
1131 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1133 const bool PvNode = (NT == PV);
1135 assert(NT == PV || NT == NonPV);
1136 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1137 assert((alpha == beta - 1) || PvNode);
1138 assert(depth <= DEPTH_ZERO);
1141 Move ttMove, move, bestMove;
1142 Value ttValue, bestValue, value, evalMargin, futilityValue, futilityBase;
1143 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1147 Value oldAlpha = alpha;
1149 ss->currentMove = bestMove = MOVE_NONE;
1150 ss->ply = (ss-1)->ply + 1;
1152 // Check for an instant draw or maximum ply reached
1153 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1156 // Decide whether or not to include checks, this fixes also the type of
1157 // TT entry depth that we are going to use. Note that in qsearch we use
1158 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1159 inCheck = pos.in_check();
1160 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1162 // Transposition table lookup. At PV nodes, we don't use the TT for
1163 // pruning, but only for move ordering.
1164 tte = TT.probe(pos.key());
1165 ttMove = (tte ? tte->move() : MOVE_NONE);
1166 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_ZERO;
1168 if (!PvNode && tte && can_return_tt(tte, ttDepth, ttValue, beta))
1170 ss->currentMove = ttMove; // Can be MOVE_NONE
1174 // Evaluate the position statically
1177 bestValue = futilityBase = -VALUE_INFINITE;
1178 ss->eval = evalMargin = VALUE_NONE;
1179 enoughMaterial = false;
1185 assert(tte->static_value() != VALUE_NONE);
1187 evalMargin = tte->static_value_margin();
1188 ss->eval = bestValue = tte->static_value();
1191 ss->eval = bestValue = evaluate(pos, evalMargin);
1193 // Stand pat. Return immediately if static value is at least beta
1194 if (bestValue >= beta)
1197 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1202 if (PvNode && bestValue > alpha)
1205 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1206 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1209 // Initialize a MovePicker object for the current position, and prepare
1210 // to search the moves. Because the depth is <= 0 here, only captures,
1211 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1213 MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
1216 // Loop through the moves until no moves remain or a beta cutoff occurs
1217 while ( bestValue < beta
1218 && (move = mp.next_move()) != MOVE_NONE)
1220 assert(is_ok(move));
1222 givesCheck = pos.move_gives_check(move, ci);
1230 && !is_promotion(move)
1231 && !pos.is_passed_pawn_push(move))
1233 futilityValue = futilityBase
1234 + PieceValueEndgame[pos.piece_on(to_sq(move))]
1235 + (is_enpassant(move) ? PawnValueEndgame : VALUE_ZERO);
1237 if (futilityValue < beta)
1239 if (futilityValue > bestValue)
1240 bestValue = futilityValue;
1245 // Prune moves with negative or equal SEE
1246 if ( futilityBase < beta
1247 && depth < DEPTH_ZERO
1248 && pos.see(move) <= 0)
1252 // Detect non-capture evasions that are candidate to be pruned
1253 evasionPrunable = !PvNode
1255 && bestValue > VALUE_MATED_IN_MAX_PLY
1256 && !pos.is_capture(move)
1257 && !pos.can_castle(pos.side_to_move());
1259 // Don't search moves with negative SEE values
1261 && (!inCheck || evasionPrunable)
1263 && !is_promotion(move)
1264 && pos.see_sign(move) < 0)
1267 // Don't search useless checks
1272 && !pos.is_capture_or_promotion(move)
1273 && ss->eval + PawnValueMidgame / 4 < beta
1274 && !check_is_dangerous(pos, move, futilityBase, beta))
1277 // Check for legality only before to do the move
1278 if (!pos.pl_move_is_legal(move, ci.pinned))
1281 ss->currentMove = move;
1283 // Make and search the move
1284 pos.do_move(move, st, ci, givesCheck);
1285 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1286 pos.undo_move(move);
1288 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1291 if (value > bestValue)
1298 && value < beta) // We want always alpha < beta
1303 // All legal moves have been searched. A special case: If we're in check
1304 // and no legal moves were found, it is checkmate.
1305 if (inCheck && bestValue == -VALUE_INFINITE)
1306 return mated_in(ss->ply); // Plies to mate from the root
1308 // Update transposition table
1309 move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
1310 bt = bestValue <= oldAlpha ? BOUND_UPPER
1311 : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
1313 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), bt, ttDepth, move, ss->eval, evalMargin);
1315 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1321 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1322 // bestValue is updated only when returning false because in that case move
1325 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta)
1327 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1328 Square from, to, ksq;
1332 from = from_sq(move);
1334 them = ~pos.side_to_move();
1335 ksq = pos.king_square(them);
1336 kingAtt = pos.attacks_from<KING>(ksq);
1337 pc = pos.piece_moved(move);
1339 occ = pos.pieces() ^ from ^ ksq;
1340 oldAtt = pos.attacks_from(pc, from, occ);
1341 newAtt = pos.attacks_from(pc, to, occ);
1343 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1344 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1346 if (!more_than_one(b))
1349 // Rule 2. Queen contact check is very dangerous
1350 if (type_of(pc) == QUEEN && (kingAtt & to))
1353 // Rule 3. Creating new double threats with checks
1354 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1357 // Note that here we generate illegal "double move"!
1358 if (futilityBase + PieceValueEndgame[pos.piece_on(pop_1st_bit(&b))] >= beta)
1366 // connected_moves() tests whether two moves are 'connected' in the sense
1367 // that the first move somehow made the second move possible (for instance
1368 // if the moving piece is the same in both moves). The first move is assumed
1369 // to be the move that was made to reach the current position, while the
1370 // second move is assumed to be a move from the current position.
1372 bool connected_moves(const Position& pos, Move m1, Move m2) {
1374 Square f1, t1, f2, t2;
1381 // Case 1: The moving piece is the same in both moves
1387 // Case 2: The destination square for m2 was vacated by m1
1393 // Case 3: Moving through the vacated square
1394 p2 = pos.piece_on(f2);
1395 if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
1398 // Case 4: The destination square for m2 is defended by the moving piece in m1
1399 p1 = pos.piece_on(t1);
1400 if (pos.attacks_from(p1, t1) & t2)
1403 // Case 5: Discovered check, checking piece is the piece moved in m1
1404 ksq = pos.king_square(pos.side_to_move());
1405 if ( piece_is_slider(p1)
1406 && (between_bb(t1, ksq) & f2)
1407 && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
1414 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1415 // "plies to mate from the current position". Non-mate scores are unchanged.
1416 // The function is called before storing a value to the transposition table.
1418 Value value_to_tt(Value v, int ply) {
1420 if (v >= VALUE_MATE_IN_MAX_PLY)
1423 if (v <= VALUE_MATED_IN_MAX_PLY)
1430 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1431 // from the transposition table (where refers to the plies to mate/be mated
1432 // from current position) to "plies to mate/be mated from the root".
1434 Value value_from_tt(Value v, int ply) {
1436 if (v >= VALUE_MATE_IN_MAX_PLY)
1439 if (v <= VALUE_MATED_IN_MAX_PLY)
1446 // connected_threat() tests whether it is safe to forward prune a move or if
1447 // is somehow connected to the threat move returned by null search.
1449 bool connected_threat(const Position& pos, Move m, Move threat) {
1452 assert(is_ok(threat));
1453 assert(!pos.is_capture_or_promotion(m));
1454 assert(!pos.is_passed_pawn_push(m));
1456 Square mfrom, mto, tfrom, tto;
1460 tfrom = from_sq(threat);
1461 tto = to_sq(threat);
1463 // Case 1: Don't prune moves which move the threatened piece
1467 // Case 2: If the threatened piece has value less than or equal to the
1468 // value of the threatening piece, don't prune moves which defend it.
1469 if ( pos.is_capture(threat)
1470 && ( PieceValueMidgame[pos.piece_on(tfrom)] >= PieceValueMidgame[pos.piece_on(tto)]
1471 || type_of(pos.piece_on(tfrom)) == KING)
1472 && pos.move_attacks_square(m, tto))
1475 // Case 3: If the moving piece in the threatened move is a slider, don't
1476 // prune safe moves which block its ray.
1477 if ( piece_is_slider(pos.piece_on(tfrom))
1478 && (between_bb(tfrom, tto) & mto)
1479 && pos.see_sign(m) >= 0)
1486 // can_return_tt() returns true if a transposition table score can be used to
1487 // cut-off at a given point in search.
1489 bool can_return_tt(const TTEntry* tte, Depth depth, Value v, Value beta) {
1491 return ( tte->depth() >= depth
1492 || v >= std::max(VALUE_MATE_IN_MAX_PLY, beta)
1493 || v < std::min(VALUE_MATED_IN_MAX_PLY, beta))
1495 && ( ((tte->type() & BOUND_LOWER) && v >= beta)
1496 || ((tte->type() & BOUND_UPPER) && v < beta));
1500 // refine_eval() returns the transposition table score if possible, otherwise
1501 // falls back on static position evaluation.
1503 Value refine_eval(const TTEntry* tte, Value v, Value defaultEval) {
1507 if ( ((tte->type() & BOUND_LOWER) && v >= defaultEval)
1508 || ((tte->type() & BOUND_UPPER) && v < defaultEval))
1515 // score_to_uci() converts a value to a string suitable for use with the UCI
1516 // protocol specifications:
1518 // cp <x> The score from the engine's point of view in centipawns.
1519 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1520 // use negative values for y.
1522 string score_to_uci(Value v, Value alpha, Value beta) {
1524 std::stringstream s;
1526 if (abs(v) < VALUE_MATE_IN_MAX_PLY)
1527 s << "cp " << v * 100 / int(PawnValueMidgame);
1529 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1531 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1537 // pv_info_to_uci() sends search info to GUI. UCI protocol requires to send all
1538 // the PV lines also if are still to be searched and so refer to the previous
1541 void pv_info_to_uci(const Position& pos, int depth, Value alpha, Value beta) {
1543 int t = SearchTime.elapsed();
1546 for (int i = 0; i < Threads.size(); i++)
1547 if (Threads[i].maxPly > selDepth)
1548 selDepth = Threads[i].maxPly;
1550 for (size_t i = 0; i < std::min(UCIMultiPV, RootMoves.size()); i++)
1552 bool updated = (i <= PVIdx);
1554 if (depth == 1 && !updated)
1557 int d = (updated ? depth : depth - 1);
1558 Value v = (updated ? RootMoves[i].score : RootMoves[i].prevScore);
1559 std::stringstream s;
1561 for (int j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1562 s << " " << move_to_uci(RootMoves[i].pv[j], Chess960);
1564 cout << "info depth " << d
1565 << " seldepth " << selDepth
1566 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1567 << " nodes " << pos.nodes_searched()
1568 << " nps " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
1570 << " multipv " << i + 1
1571 << " pv" << s.str() << endl;
1576 // pv_info_to_log() writes human-readable search information to the log file
1577 // (which is created when the UCI parameter "Use Search Log" is "true"). It
1578 // uses the two below helpers to pretty format time and score respectively.
1580 string time_to_string(int millisecs) {
1582 const int MSecMinute = 1000 * 60;
1583 const int MSecHour = 1000 * 60 * 60;
1585 int hours = millisecs / MSecHour;
1586 int minutes = (millisecs % MSecHour) / MSecMinute;
1587 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1589 std::stringstream s;
1594 s << std::setfill('0') << std::setw(2) << minutes << ':'
1595 << std::setw(2) << seconds;
1599 string score_to_string(Value v) {
1601 std::stringstream s;
1603 if (v >= VALUE_MATE_IN_MAX_PLY)
1604 s << "#" << (VALUE_MATE - v + 1) / 2;
1605 else if (v <= VALUE_MATED_IN_MAX_PLY)
1606 s << "-#" << (VALUE_MATE + v) / 2;
1608 s << std::setprecision(2) << std::fixed << std::showpos
1609 << float(v) / PawnValueMidgame;
1614 void pv_info_to_log(Position& pos, int depth, Value value, int time, Move pv[]) {
1616 const int64_t K = 1000;
1617 const int64_t M = 1000000;
1619 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1621 string san, padding;
1623 std::stringstream s;
1625 s << std::setw(2) << depth
1626 << std::setw(8) << score_to_string(value)
1627 << std::setw(8) << time_to_string(time);
1629 if (pos.nodes_searched() < M)
1630 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1632 else if (pos.nodes_searched() < K * M)
1633 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1636 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1638 padding = string(s.str().length(), ' ');
1639 length = padding.length();
1641 while (*m != MOVE_NONE)
1643 san = move_to_san(pos, *m);
1645 if (length + san.length() > 80)
1647 s << "\n" + padding;
1648 length = padding.length();
1652 length += san.length() + 1;
1654 pos.do_move(*m++, *st++);
1658 pos.undo_move(*--m);
1660 Log l(Options["Search Log Filename"]);
1661 l << s.str() << endl;
1665 // When playing with strength handicap choose best move among the MultiPV set
1666 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1668 Move do_skill_level() {
1670 assert(MultiPV > 1);
1674 // PRNG sequence should be not deterministic
1675 for (int i = Time::current_time().msec() % 50; i > 0; i--)
1676 rk.rand<unsigned>();
1678 // RootMoves are already sorted by score in descending order
1679 size_t size = std::min(MultiPV, RootMoves.size());
1680 int variance = std::min(RootMoves[0].score - RootMoves[size - 1].score, PawnValueMidgame);
1681 int weakness = 120 - 2 * SkillLevel;
1682 int max_s = -VALUE_INFINITE;
1683 Move best = MOVE_NONE;
1685 // Choose best move. For each move score we add two terms both dependent on
1686 // weakness, one deterministic and bigger for weaker moves, and one random,
1687 // then we choose the move with the resulting highest score.
1688 for (size_t i = 0; i < size; i++)
1690 int s = RootMoves[i].score;
1692 // Don't allow crazy blunders even at very low skills
1693 if (i > 0 && RootMoves[i-1].score > s + EasyMoveMargin)
1696 // This is our magic formula
1697 s += ( weakness * int(RootMoves[0].score - s)
1698 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1703 best = RootMoves[i].pv[0];
1712 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1713 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1714 /// allow to always have a ponder move even when we fail high at root, and a
1715 /// long PV to print that is important for position analysis.
1717 void RootMove::extract_pv_from_tt(Position& pos) {
1719 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1724 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1728 pos.do_move(m, *st++);
1730 while ( (tte = TT.probe(pos.key())) != NULL
1731 && (m = tte->move()) != MOVE_NONE // Local copy, TT entry could change
1732 && pos.is_pseudo_legal(m)
1733 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1735 && (!pos.is_draw<false>() || ply < 2))
1738 pos.do_move(m, *st++);
1741 pv.push_back(MOVE_NONE);
1743 do pos.undo_move(pv[--ply]); while (ply);
1747 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1748 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1749 /// first, even if the old TT entries have been overwritten.
1751 void RootMove::insert_pv_in_tt(Position& pos) {
1753 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1756 Value v, m = VALUE_NONE;
1759 assert(pv[ply] != MOVE_NONE && pos.is_pseudo_legal(pv[ply]));
1765 // Don't overwrite existing correct entries
1766 if (!tte || tte->move() != pv[ply])
1768 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
1769 TT.store(k, VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
1771 pos.do_move(pv[ply], *st++);
1773 } while (pv[++ply] != MOVE_NONE);
1775 do pos.undo_move(pv[--ply]); while (ply);
1779 /// Thread::idle_loop() is where the thread is parked when it has no work to do.
1780 /// The parameter 'master_sp', if non-NULL, is a pointer to an active SplitPoint
1781 /// object for which the thread is the master.
1783 void Thread::idle_loop(SplitPoint* sp_master) {
1785 // If this thread is the master of a split point and all slaves have
1786 // finished their work at this split point, return from the idle loop.
1787 while (!sp_master || sp_master->slavesMask)
1789 // If we are not searching, wait for a condition to be signaled
1790 // instead of wasting CPU time polling for work.
1793 || (!is_searching && Threads.use_sleeping_threads()))
1801 // Grab the lock to avoid races with Thread::wake_up()
1802 lock_grab(sleepLock);
1804 // If we are master and all slaves have finished don't go to sleep
1805 if (sp_master && !sp_master->slavesMask)
1807 lock_release(sleepLock);
1811 // Do sleep after retesting sleep conditions under lock protection, in
1812 // particular we need to avoid a deadlock in case a master thread has,
1813 // in the meanwhile, allocated us and sent the wake_up() call before we
1814 // had the chance to grab the lock.
1815 if (do_sleep || !is_searching)
1816 cond_wait(sleepCond, sleepLock);
1818 lock_release(sleepLock);
1821 // If this thread has been assigned work, launch a search
1824 assert(!do_sleep && !do_exit);
1826 lock_grab(Threads.splitLock);
1828 assert(is_searching);
1829 SplitPoint* sp = curSplitPoint;
1831 lock_release(Threads.splitLock);
1833 Stack ss[MAX_PLY_PLUS_2];
1834 Position pos(*sp->pos, this);
1836 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1839 lock_grab(sp->lock);
1841 if (sp->nodeType == Root)
1842 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1843 else if (sp->nodeType == PV)
1844 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1845 else if (sp->nodeType == NonPV)
1846 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1850 assert(is_searching);
1852 is_searching = false;
1853 sp->slavesMask &= ~(1ULL << idx);
1854 sp->nodes += pos.nodes_searched();
1856 // Wake up master thread so to allow it to return from the idle loop in
1857 // case we are the last slave of the split point.
1858 if ( Threads.use_sleeping_threads()
1859 && this != sp->master
1860 && !sp->master->is_searching)
1861 sp->master->wake_up();
1863 // After releasing the lock we cannot access anymore any SplitPoint
1864 // related data in a safe way becuase it could have been released under
1865 // our feet by the sp master. Also accessing other Thread objects is
1866 // unsafe because if we are exiting there is a chance are already freed.
1867 lock_release(sp->lock);
1873 /// check_time() is called by the timer thread when the timer triggers. It is
1874 /// used to print debug info and, more important, to detect when we are out of
1875 /// available time and so stop the search.
1879 static Time lastInfoTime = Time::current_time();
1881 if (lastInfoTime.elapsed() >= 1000)
1883 lastInfoTime.restart();
1890 int e = SearchTime.elapsed();
1891 bool stillAtFirstMove = Signals.firstRootMove
1892 && !Signals.failedLowAtRoot
1893 && e > TimeMgr.available_time();
1895 bool noMoreTime = e > TimeMgr.maximum_time() - 2 * TimerResolution
1896 || stillAtFirstMove;
1898 if ( (Limits.use_time_management() && noMoreTime)
1899 || (Limits.movetime && e >= Limits.movetime))
1900 Signals.stop = true;