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/>.
36 #include "ucioption.h"
40 volatile SignalsType Signals;
42 std::vector<RootMove> RootMoves;
45 Time::point SearchTime;
46 StateStackPtr SetupStates;
51 using namespace Search;
55 // Set to true to force running with one thread. Used for debugging
56 const bool FakeSplit = false;
58 // This is the minimum interval in msec between two check_time() calls
59 const int TimerResolution = 5;
61 // Different node types, used as template parameter
62 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
64 // Dynamic razoring margin based on depth
65 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
67 // Futility lookup tables (initialized at startup) and their access functions
68 Value FutilityMargins[16][64]; // [depth][moveNumber]
69 int FutilityMoveCounts[32]; // [depth]
71 inline Value futility_margin(Depth d, int mn) {
73 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
77 // Reduction lookup tables (initialized at startup) and their access function
78 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
80 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
82 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
88 Value DrawValue[COLOR_NB];
92 template <NodeType NT>
93 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
95 template <NodeType NT, bool InCheck>
96 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
98 void id_loop(Position& pos);
99 Value value_to_tt(Value v, int ply);
100 Value value_from_tt(Value v, int ply);
101 bool check_is_dangerous(Position& pos, Move move, Value futilityBase, Value beta);
102 bool allows_move(const Position& pos, Move first, Move second);
103 bool prevents_move(const Position& pos, Move first, Move second);
104 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
107 Skill(int l) : level(l), best(MOVE_NONE) {}
109 if (enabled()) // Swap best PV line with the sub-optimal one
110 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
111 RootMoves.end(), best ? best : pick_move()));
114 bool enabled() const { return level < 20; }
115 bool time_to_pick(int depth) const { return depth == 1 + level; }
125 /// Search::init() is called during startup to initialize various lookup tables
127 void Search::init() {
129 int d; // depth (ONE_PLY == 2)
130 int hd; // half depth (ONE_PLY == 1)
133 // Init reductions array
134 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
136 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
137 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
138 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
139 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
142 // Init futility margins array
143 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
144 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
146 // Init futility move count array
147 for (d = 0; d < 32; d++)
148 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(double(d), 2.0));
152 /// Search::perft() is our utility to verify move generation. All the leaf nodes
153 /// up to the given depth are generated and counted and the sum returned.
155 size_t Search::perft(Position& pos, Depth depth) {
157 // At the last ply just return the number of legal moves (leaf nodes)
158 if (depth == ONE_PLY)
159 return MoveList<LEGAL>(pos).size();
165 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
167 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
168 cnt += perft(pos, depth - ONE_PLY);
169 pos.undo_move(ml.move());
176 /// Search::think() is the external interface to Stockfish's search, and is
177 /// called by the main thread when the program receives the UCI 'go' command. It
178 /// searches from RootPos and at the end prints the "bestmove" to output.
180 void Search::think() {
182 static PolyglotBook book; // Defined static to initialize the PRNG only once
184 RootColor = RootPos.side_to_move();
185 TimeMgr.init(Limits, RootPos.startpos_ply_counter(), RootColor);
187 if (RootMoves.empty())
189 RootMoves.push_back(MOVE_NONE);
190 sync_cout << "info depth 0 score "
191 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
197 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
199 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
201 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
203 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
208 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
210 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
211 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
212 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
213 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
216 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
218 if (Options["Use Search Log"])
220 Log log(Options["Search Log Filename"]);
221 log << "\nSearching: " << RootPos.fen()
222 << "\ninfinite: " << Limits.infinite
223 << " ponder: " << Limits.ponder
224 << " time: " << Limits.time[RootColor]
225 << " increment: " << Limits.inc[RootColor]
226 << " moves to go: " << Limits.movestogo
230 // Reset the threads, still sleeping: will be wake up at split time
231 for (size_t i = 0; i < Threads.size(); i++)
232 Threads[i].maxPly = 0;
234 Threads.sleepWhileIdle = Options["Use Sleeping Threads"];
236 // Set best timer interval to avoid lagging under time pressure. Timer is
237 // used to check for remaining available thinking time.
238 Threads.timer_thread()->msec =
239 Limits.use_time_management() ? std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)) :
240 Limits.nodes ? 2 * TimerResolution
243 Threads.timer_thread()->notify_one(); // Wake up the recurring timer
245 id_loop(RootPos); // Let's start searching !
247 Threads.timer_thread()->msec = 0; // Stop the timer
248 Threads.sleepWhileIdle = true; // Send idle threads to sleep
250 if (Options["Use Search Log"])
252 Time::point elapsed = Time::now() - SearchTime + 1;
254 Log log(Options["Search Log Filename"]);
255 log << "Nodes: " << RootPos.nodes_searched()
256 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
257 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
260 RootPos.do_move(RootMoves[0].pv[0], st);
261 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
262 RootPos.undo_move(RootMoves[0].pv[0]);
267 // When we reach max depth we arrive here even without Signals.stop is raised,
268 // but if we are pondering or in infinite search, according to UCI protocol,
269 // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
270 // command. We simply wait here until GUI sends one of those commands (that
271 // raise Signals.stop).
272 if (!Signals.stop && (Limits.ponder || Limits.infinite))
274 Signals.stopOnPonderhit = true;
275 RootPos.this_thread()->wait_for(Signals.stop);
278 // Best move could be MOVE_NONE when searching on a stalemate position
279 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
280 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
287 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
288 // with increasing depth until the allocated thinking time has been consumed,
289 // user stops the search, or the maximum search depth is reached.
291 void id_loop(Position& pos) {
293 Stack ss[MAX_PLY_PLUS_2];
294 int depth, prevBestMoveChanges;
295 Value bestValue, alpha, beta, delta;
296 bool bestMoveNeverChanged = true;
298 memset(ss, 0, 4 * sizeof(Stack));
299 depth = BestMoveChanges = 0;
300 bestValue = delta = -VALUE_INFINITE;
301 ss->currentMove = MOVE_NULL; // Hack to skip update gains
306 PVSize = Options["MultiPV"];
307 Skill skill(Options["Skill Level"]);
309 // Do we have to play with skill handicap? In this case enable MultiPV search
310 // that we will use behind the scenes to retrieve a set of possible moves.
311 if (skill.enabled() && PVSize < 4)
314 PVSize = std::min(PVSize, RootMoves.size());
316 // Iterative deepening loop until requested to stop or target depth reached
317 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
319 // Save last iteration's scores before first PV line is searched and all
320 // the move scores but the (new) PV are set to -VALUE_INFINITE.
321 for (size_t i = 0; i < RootMoves.size(); i++)
322 RootMoves[i].prevScore = RootMoves[i].score;
324 prevBestMoveChanges = BestMoveChanges; // Only sensible when PVSize == 1
327 // MultiPV loop. We perform a full root search for each PV line
328 for (PVIdx = 0; PVIdx < PVSize; PVIdx++)
330 // Set aspiration window default width
331 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
334 alpha = RootMoves[PVIdx].prevScore - delta;
335 beta = RootMoves[PVIdx].prevScore + delta;
339 alpha = -VALUE_INFINITE;
340 beta = VALUE_INFINITE;
343 // Start with a small aspiration window and, in case of fail high/low,
344 // research with bigger window until not failing high/low anymore.
347 // Search starts from ss+1 to allow referencing (ss-1). This is
348 // needed by update gains and ss copy when splitting at Root.
349 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
351 // Bring to front the best move. It is critical that sorting is
352 // done with a stable algorithm because all the values but the first
353 // and eventually the new best one are set to -VALUE_INFINITE and
354 // we want to keep the same order for all the moves but the new
355 // PV that goes to the front. Note that in case of MultiPV search
356 // the already searched PV lines are preserved.
357 sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
359 // Write PV back to transposition table in case the relevant
360 // entries have been overwritten during the search.
361 for (size_t i = 0; i <= PVIdx; i++)
362 RootMoves[i].insert_pv_in_tt(pos);
364 // If search has been stopped return immediately. Sorting and
365 // writing PV back to TT is safe becuase RootMoves is still
366 // valid, although refers to previous iteration.
370 // In case of failing high/low increase aspiration window and
371 // research, otherwise exit the loop.
372 if (bestValue > alpha && bestValue < beta)
375 // Give some update (without cluttering the UI) before to research
376 if (Time::now() - SearchTime > 3000)
377 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
379 if (abs(bestValue) >= VALUE_KNOWN_WIN)
381 alpha = -VALUE_INFINITE;
382 beta = VALUE_INFINITE;
384 else if (bestValue >= beta)
391 Signals.failedLowAtRoot = true;
392 Signals.stopOnPonderhit = false;
398 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
401 // Sort the PV lines searched so far and update the GUI
402 sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
403 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
404 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
407 // Do we need to pick now the sub-optimal best move ?
408 if (skill.enabled() && skill.time_to_pick(depth))
411 if (Options["Use Search Log"])
413 Log log(Options["Search Log Filename"]);
414 log << pretty_pv(pos, depth, bestValue, Time::now() - SearchTime, &RootMoves[0].pv[0])
418 // Filter out startup noise when monitoring best move stability
419 if (depth > 2 && BestMoveChanges)
420 bestMoveNeverChanged = false;
422 // Do we have found a "mate in x"?
424 && bestValue >= VALUE_MATE_IN_MAX_PLY
425 && VALUE_MATE - bestValue <= 2 * Limits.mate)
428 // Do we have time for the next iteration? Can we stop searching now?
429 if (Limits.use_time_management() && !Signals.stopOnPonderhit)
431 bool stop = false; // Local variable, not the volatile Signals.stop
433 // Take in account some extra time if the best move has changed
434 if (depth > 4 && depth < 50 && PVSize == 1)
435 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
437 // Stop search if most of available time is already consumed. We
438 // probably don't have enough time to search the first move at the
439 // next iteration anyway.
440 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
443 // Stop search early if one move seems to be much better than others
447 && ( (bestMoveNeverChanged && pos.captured_piece_type())
448 || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
450 Value rBeta = bestValue - 2 * PawnValueMg;
451 (ss+1)->excludedMove = RootMoves[0].pv[0];
452 (ss+1)->skipNullMove = true;
453 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
454 (ss+1)->skipNullMove = false;
455 (ss+1)->excludedMove = MOVE_NONE;
463 // If we are allowed to ponder do not stop the search now but
464 // keep pondering until GUI sends "ponderhit" or "stop".
466 Signals.stopOnPonderhit = true;
475 // search<>() is the main search function for both PV and non-PV nodes and for
476 // normal and SplitPoint nodes. When called just after a split point the search
477 // is simpler because we have already probed the hash table, done a null move
478 // search, and searched the first move before splitting, we don't have to repeat
479 // all this work again. We also don't need to store anything to the hash table
480 // here: This is taken care of after we return from the split point.
482 template <NodeType NT>
483 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
485 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
486 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
487 const bool RootNode = (NT == Root || NT == SplitPointRoot);
489 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
490 assert(PvNode || (alpha == beta - 1));
491 assert(depth > DEPTH_ZERO);
493 Move movesSearched[64];
498 Move ttMove, move, excludedMove, bestMove, threatMove;
500 Value bestValue, value, ttValue;
501 Value eval, nullValue, futilityValue;
502 bool inCheck, givesCheck, pvMove, singularExtensionNode;
503 bool captureOrPromotion, dangerous, doFullDepthSearch;
504 int moveCount, playedMoveCount;
506 // Step 1. Initialize node
507 Thread* thisThread = pos.this_thread();
508 moveCount = playedMoveCount = 0;
509 inCheck = pos.checkers();
514 bestMove = sp->bestMove;
515 threatMove = sp->threatMove;
516 bestValue = sp->bestValue;
518 ttMove = excludedMove = MOVE_NONE;
519 ttValue = VALUE_NONE;
521 assert(sp->bestValue > -VALUE_INFINITE && sp->moveCount > 0);
523 goto split_point_start;
526 bestValue = -VALUE_INFINITE;
527 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
528 ss->ply = (ss-1)->ply + 1;
529 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
530 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
532 // Used to send selDepth info to GUI
533 if (PvNode && thisThread->maxPly < ss->ply)
534 thisThread->maxPly = ss->ply;
538 // Step 2. Check for aborted search and immediate draw
539 if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
540 return DrawValue[pos.side_to_move()];
542 // Step 3. Mate distance pruning. Even if we mate at the next move our score
543 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
544 // a shorter mate was found upward in the tree then there is no need to search
545 // further, we will never beat current alpha. Same logic but with reversed signs
546 // applies also in the opposite condition of being mated instead of giving mate,
547 // in this case return a fail-high score.
548 alpha = std::max(mated_in(ss->ply), alpha);
549 beta = std::min(mate_in(ss->ply+1), beta);
554 // Step 4. Transposition table lookup
555 // We don't want the score of a partial search to overwrite a previous full search
556 // TT value, so we use a different position key in case of an excluded move.
557 excludedMove = ss->excludedMove;
558 posKey = excludedMove ? pos.exclusion_key() : pos.key();
559 tte = TT.probe(posKey);
560 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
561 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
563 // At PV nodes we check for exact scores, while at non-PV nodes we check for
564 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
565 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
566 // we should also update RootMoveList to avoid bogus output.
569 && tte->depth() >= depth
570 && ttValue != VALUE_NONE // Only in case of TT access race
571 && ( PvNode ? tte->type() == BOUND_EXACT
572 : ttValue >= beta ? (tte->type() & BOUND_LOWER)
573 : (tte->type() & BOUND_UPPER)))
576 ss->currentMove = ttMove; // Can be MOVE_NONE
580 && !pos.is_capture_or_promotion(ttMove)
581 && ttMove != ss->killers[0])
583 ss->killers[1] = ss->killers[0];
584 ss->killers[0] = ttMove;
589 // Step 5. Evaluate the position statically and update parent's gain statistics
591 ss->staticEval = ss->evalMargin = eval = VALUE_NONE;
595 // Never assume anything on values stored in TT
596 if ( (ss->staticEval = eval = tte->static_value()) == VALUE_NONE
597 ||(ss->evalMargin = tte->static_value_margin()) == VALUE_NONE)
598 eval = ss->staticEval = evaluate(pos, ss->evalMargin);
600 // Can ttValue be used as a better position evaluation?
601 if (ttValue != VALUE_NONE)
602 if ( ((tte->type() & BOUND_LOWER) && ttValue > eval)
603 || ((tte->type() & BOUND_UPPER) && ttValue < eval))
608 eval = ss->staticEval = evaluate(pos, ss->evalMargin);
609 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
610 ss->staticEval, ss->evalMargin);
613 // Update gain for the parent non-capture move given the static position
614 // evaluation before and after the move.
615 if ( (move = (ss-1)->currentMove) != MOVE_NULL
616 && (ss-1)->staticEval != VALUE_NONE
617 && ss->staticEval != VALUE_NONE
618 && !pos.captured_piece_type()
619 && type_of(move) == NORMAL)
621 Square to = to_sq(move);
622 Gain.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
625 // Step 6. Razoring (is omitted in PV nodes)
627 && depth < 4 * ONE_PLY
629 && eval + razor_margin(depth) < beta
630 && ttMove == MOVE_NONE
631 && abs(beta) < VALUE_MATE_IN_MAX_PLY
632 && !pos.pawn_on_7th(pos.side_to_move()))
634 Value rbeta = beta - razor_margin(depth);
635 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
637 // Logically we should return (v + razor_margin(depth)), but
638 // surprisingly this did slightly weaker in tests.
642 // Step 7. Static null move pruning (is omitted in PV nodes)
643 // We're betting that the opponent doesn't have a move that will reduce
644 // the score by more than futility_margin(depth) if we do a null move.
647 && depth < 4 * ONE_PLY
649 && eval - FutilityMargins[depth][0] >= beta
650 && abs(beta) < VALUE_MATE_IN_MAX_PLY
651 && pos.non_pawn_material(pos.side_to_move()))
652 return eval - FutilityMargins[depth][0];
654 // Step 8. Null move search with verification search (is omitted in PV nodes)
660 && abs(beta) < VALUE_MATE_IN_MAX_PLY
661 && pos.non_pawn_material(pos.side_to_move()))
663 ss->currentMove = MOVE_NULL;
665 // Null move dynamic reduction based on depth
666 Depth R = 3 * ONE_PLY + depth / 4;
668 // Null move dynamic reduction based on value
669 if (eval - PawnValueMg > beta)
672 pos.do_null_move(st);
673 (ss+1)->skipNullMove = true;
674 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
675 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
676 (ss+1)->skipNullMove = false;
677 pos.undo_null_move();
679 if (nullValue >= beta)
681 // Do not return unproven mate scores
682 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
685 if (depth < 6 * ONE_PLY)
688 // Do verification search at high depths
689 ss->skipNullMove = true;
690 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
691 ss->skipNullMove = false;
698 // The null move failed low, which means that we may be faced with
699 // some kind of threat. If the previous move was reduced, check if
700 // the move that refuted the null move was somehow connected to the
701 // move which was reduced. If a connection is found, return a fail
702 // low score (which will cause the reduced move to fail high in the
703 // parent node, which will trigger a re-search with full depth).
704 threatMove = (ss+1)->currentMove;
706 if ( depth < 5 * ONE_PLY
708 && threatMove != MOVE_NONE
709 && allows_move(pos, (ss-1)->currentMove, threatMove))
714 // Step 9. ProbCut (is omitted in PV nodes)
715 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
716 // and a reduced search returns a value much above beta, we can (almost) safely
717 // prune the previous move.
719 && depth >= 5 * ONE_PLY
722 && excludedMove == MOVE_NONE
723 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
725 Value rbeta = beta + 200;
726 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
728 assert(rdepth >= ONE_PLY);
729 assert((ss-1)->currentMove != MOVE_NONE);
730 assert((ss-1)->currentMove != MOVE_NULL);
732 MovePicker mp(pos, ttMove, Hist, pos.captured_piece_type());
735 while ((move = mp.next_move<false>()) != MOVE_NONE)
736 if (pos.pl_move_is_legal(move, ci.pinned))
738 ss->currentMove = move;
739 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
740 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
747 // Step 10. Internal iterative deepening
748 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
749 && ttMove == MOVE_NONE
750 && (PvNode || (!inCheck && ss->staticEval + Value(256) >= beta)))
752 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
754 ss->skipNullMove = true;
755 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
756 ss->skipNullMove = false;
758 tte = TT.probe(posKey);
759 ttMove = tte ? tte->move() : MOVE_NONE;
762 split_point_start: // At split points actual search starts from here
764 MovePicker mp(pos, ttMove, depth, Hist, ss, PvNode ? -VALUE_INFINITE : beta);
766 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
767 singularExtensionNode = !RootNode
769 && depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)
770 && ttMove != MOVE_NONE
771 && !excludedMove // Recursive singular search is not allowed
772 && (tte->type() & BOUND_LOWER)
773 && tte->depth() >= depth - 3 * ONE_PLY;
775 // Step 11. Loop through moves
776 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
777 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
781 if (move == excludedMove)
784 // At root obey the "searchmoves" option and skip moves not listed in Root
785 // Move List, as a consequence any illegal move is also skipped. In MultiPV
786 // mode we also skip PV moves which have been already searched.
787 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
792 // Shared counter cannot be decremented later if move turns out to be illegal
793 if (!pos.pl_move_is_legal(move, ci.pinned))
796 moveCount = ++sp->moveCount;
804 Signals.firstRootMove = (moveCount == 1);
806 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 3000)
807 sync_cout << "info depth " << depth / ONE_PLY
808 << " currmove " << move_to_uci(move, pos.is_chess960())
809 << " currmovenumber " << moveCount + PVIdx << sync_endl;
813 captureOrPromotion = pos.is_capture_or_promotion(move);
814 givesCheck = pos.move_gives_check(move, ci);
815 dangerous = givesCheck
816 || pos.is_passed_pawn_push(move)
817 || type_of(move) == CASTLE
818 || ( captureOrPromotion // Entering a pawn endgame?
819 && type_of(pos.piece_on(to_sq(move))) != PAWN
820 && type_of(move) == NORMAL
821 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
822 - PieceValue[MG][pos.piece_on(to_sq(move))] == VALUE_ZERO));
824 // Step 12. Extend checks and, in PV nodes, also dangerous moves
825 if (PvNode && dangerous)
828 else if (givesCheck && pos.see_sign(move) >= 0)
831 // Singular extension search. If all moves but one fail low on a search of
832 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
833 // is singular and should be extended. To verify this we do a reduced search
834 // on all the other moves but the ttMove, if result is lower than ttValue minus
835 // a margin then we extend ttMove.
836 if ( singularExtensionNode
839 && pos.pl_move_is_legal(move, ci.pinned)
840 && abs(ttValue) < VALUE_KNOWN_WIN)
842 assert(ttValue != VALUE_NONE);
844 Value rBeta = ttValue - int(depth);
845 ss->excludedMove = move;
846 ss->skipNullMove = true;
847 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
848 ss->skipNullMove = false;
849 ss->excludedMove = MOVE_NONE;
855 // Update current move (this must be done after singular extension search)
856 newDepth = depth - ONE_PLY + ext;
858 // Step 13. Futility pruning (is omitted in PV nodes)
860 && !captureOrPromotion
864 && (bestValue > VALUE_MATED_IN_MAX_PLY || ( bestValue == -VALUE_INFINITE
865 && alpha > VALUE_MATED_IN_MAX_PLY)))
867 // Move count based pruning
868 if ( depth < 16 * ONE_PLY
869 && moveCount >= FutilityMoveCounts[depth]
870 && (!threatMove || !prevents_move(pos, move, threatMove)))
878 // Value based pruning
879 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
880 // but fixing this made program slightly weaker.
881 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
882 futilityValue = ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
883 + Gain[pos.piece_moved(move)][to_sq(move)];
885 if (futilityValue < beta)
893 // Prune moves with negative SEE at low depths
894 if ( predictedDepth < 2 * ONE_PLY
895 && pos.see_sign(move) < 0)
904 // Check for legality only before to do the move
905 if (!RootNode && !SpNode && !pos.pl_move_is_legal(move, ci.pinned))
911 pvMove = PvNode && moveCount == 1;
912 ss->currentMove = move;
913 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
914 movesSearched[playedMoveCount++] = move;
916 // Step 14. Make the move
917 pos.do_move(move, st, ci, givesCheck);
919 // Step 15. Reduced depth search (LMR). If the move fails high will be
920 // re-searched at full depth.
921 if ( depth > 3 * ONE_PLY
923 && !captureOrPromotion
925 && ss->killers[0] != move
926 && ss->killers[1] != move)
928 ss->reduction = reduction<PvNode>(depth, moveCount);
929 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
930 alpha = SpNode ? sp->alpha : alpha;
932 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
934 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
935 ss->reduction = DEPTH_ZERO;
938 doFullDepthSearch = !pvMove;
940 // Step 16. Full depth search, when LMR is skipped or fails high
941 if (doFullDepthSearch)
943 alpha = SpNode ? sp->alpha : alpha;
944 value = newDepth < ONE_PLY ?
945 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
946 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
947 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
950 // Only for PV nodes do a full PV search on the first move or after a fail
951 // high, in the latter case search only if value < beta, otherwise let the
952 // parent node to fail low with value <= alpha and to try another move.
953 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
954 value = newDepth < ONE_PLY ?
955 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
956 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
957 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
958 // Step 17. Undo move
961 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
963 // Step 18. Check for new best move
967 bestValue = sp->bestValue;
971 // Finished searching the move. If Signals.stop is true, the search
972 // was aborted because the user interrupted the search or because we
973 // ran out of time. In this case, the return value of the search cannot
974 // be trusted, and we don't update the best move and/or PV.
975 if (Signals.stop || thisThread->cutoff_occurred())
976 return value; // To avoid returning VALUE_INFINITE
980 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
982 // PV move or new best move ?
983 if (pvMove || value > alpha)
986 rm.extract_pv_from_tt(pos);
988 // We record how often the best move has been changed in each
989 // iteration. This information is used for time management: When
990 // the best move changes frequently, we allocate some more time.
995 // All other moves but the PV are set to the lowest value, this
996 // is not a problem when sorting becuase sort is stable and move
997 // position in the list is preserved, just the PV is pushed up.
998 rm.score = -VALUE_INFINITE;
1001 if (value > bestValue)
1003 bestValue = SpNode ? sp->bestValue = value : value;
1007 bestMove = SpNode ? sp->bestMove = move : move;
1009 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1010 alpha = SpNode ? sp->alpha = value : value;
1013 assert(value >= beta); // Fail high
1023 // Step 19. Check for splitting the search
1025 && depth >= Threads.minimumSplitDepth
1026 && Threads.slave_available(thisThread)
1027 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1029 assert(bestValue < beta);
1031 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
1032 depth, threatMove, moveCount, mp, NT);
1033 if (bestValue >= beta)
1041 // Step 20. Check for mate and stalemate
1042 // All legal moves have been searched and if there are no legal moves, it
1043 // must be mate or stalemate. Note that we can have a false positive in
1044 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1045 // harmless because return value is discarded anyhow in the parent nodes.
1046 // If we are in a singular extension search then return a fail low score.
1047 // A split node has at least one move, the one tried before to be splitted.
1049 return excludedMove ? alpha
1050 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1052 // If we have pruned all the moves without searching return a fail-low score
1053 if (bestValue == -VALUE_INFINITE)
1055 assert(!playedMoveCount);
1060 if (bestValue >= beta) // Failed high
1062 TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
1063 bestMove, ss->staticEval, ss->evalMargin);
1065 if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
1067 if (bestMove != ss->killers[0])
1069 ss->killers[1] = ss->killers[0];
1070 ss->killers[0] = bestMove;
1073 // Increase history value of the cut-off move
1074 Value bonus = Value(int(depth) * int(depth));
1075 Hist.update(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
1077 // Decrease history of all the other played non-capture moves
1078 for (int i = 0; i < playedMoveCount - 1; i++)
1080 Move m = movesSearched[i];
1081 Hist.update(pos.piece_moved(m), to_sq(m), -bonus);
1085 else // Failed low or PV search
1086 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1087 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
1088 depth, bestMove, ss->staticEval, ss->evalMargin);
1090 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1096 // qsearch() is the quiescence search function, which is called by the main
1097 // search function when the remaining depth is zero (or, to be more precise,
1098 // less than ONE_PLY).
1100 template <NodeType NT, bool InCheck>
1101 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1103 const bool PvNode = (NT == PV);
1105 assert(NT == PV || NT == NonPV);
1106 assert(InCheck == !!pos.checkers());
1107 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1108 assert(PvNode || (alpha == beta - 1));
1109 assert(depth <= DEPTH_ZERO);
1114 Move ttMove, move, bestMove;
1115 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1116 bool givesCheck, enoughMaterial, evasionPrunable;
1119 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1123 ss->currentMove = bestMove = MOVE_NONE;
1124 ss->ply = (ss-1)->ply + 1;
1126 // Check for an instant draw or maximum ply reached
1127 if (pos.is_draw<true>() || ss->ply > MAX_PLY)
1128 return DrawValue[pos.side_to_move()];
1130 // Transposition table lookup. At PV nodes, we don't use the TT for
1131 // pruning, but only for move ordering.
1133 tte = TT.probe(posKey);
1134 ttMove = tte ? tte->move() : MOVE_NONE;
1135 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1137 // Decide whether or not to include checks, this fixes also the type of
1138 // TT entry depth that we are going to use. Note that in qsearch we use
1139 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1140 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1141 : DEPTH_QS_NO_CHECKS;
1143 && tte->depth() >= ttDepth
1144 && ttValue != VALUE_NONE // Only in case of TT access race
1145 && ( PvNode ? tte->type() == BOUND_EXACT
1146 : ttValue >= beta ? (tte->type() & BOUND_LOWER)
1147 : (tte->type() & BOUND_UPPER)))
1149 ss->currentMove = ttMove; // Can be MOVE_NONE
1153 // Evaluate the position statically
1156 ss->staticEval = ss->evalMargin = VALUE_NONE;
1157 bestValue = futilityBase = -VALUE_INFINITE;
1158 enoughMaterial = false;
1164 // Never assume anything on values stored in TT
1165 if ( (ss->staticEval = bestValue = tte->static_value()) == VALUE_NONE
1166 ||(ss->evalMargin = tte->static_value_margin()) == VALUE_NONE)
1167 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
1170 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
1172 // Stand pat. Return immediately if static value is at least beta
1173 if (bestValue >= beta)
1176 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1177 DEPTH_NONE, MOVE_NONE, ss->staticEval, ss->evalMargin);
1182 if (PvNode && bestValue > alpha)
1185 futilityBase = ss->staticEval + ss->evalMargin + Value(128);
1186 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1189 // Initialize a MovePicker object for the current position, and prepare
1190 // to search the moves. Because the depth is <= 0 here, only captures,
1191 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1193 MovePicker mp(pos, ttMove, depth, Hist, to_sq((ss-1)->currentMove));
1196 // Loop through the moves until no moves remain or a beta cutoff occurs
1197 while ((move = mp.next_move<false>()) != MOVE_NONE)
1199 assert(is_ok(move));
1201 givesCheck = pos.move_gives_check(move, ci);
1209 && type_of(move) != PROMOTION
1210 && !pos.is_passed_pawn_push(move))
1212 futilityValue = futilityBase
1213 + PieceValue[EG][pos.piece_on(to_sq(move))]
1214 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1216 if (futilityValue < beta)
1218 bestValue = std::max(bestValue, futilityValue);
1222 // Prune moves with negative or equal SEE
1223 if ( futilityBase < beta
1224 && depth < DEPTH_ZERO
1225 && pos.see(move) <= 0)
1227 bestValue = std::max(bestValue, futilityBase);
1232 // Detect non-capture evasions that are candidate to be pruned
1233 evasionPrunable = !PvNode
1235 && bestValue > VALUE_MATED_IN_MAX_PLY
1236 && !pos.is_capture(move)
1237 && !pos.can_castle(pos.side_to_move());
1239 // Don't search moves with negative SEE values
1241 && (!InCheck || evasionPrunable)
1243 && type_of(move) != PROMOTION
1244 && pos.see_sign(move) < 0)
1247 // Don't search useless checks
1252 && !pos.is_capture_or_promotion(move)
1253 && ss->staticEval + PawnValueMg / 4 < beta
1254 && !check_is_dangerous(pos, move, futilityBase, beta))
1257 // Check for legality only before to do the move
1258 if (!pos.pl_move_is_legal(move, ci.pinned))
1261 ss->currentMove = move;
1263 // Make and search the move
1264 pos.do_move(move, st, ci, givesCheck);
1265 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1266 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1267 pos.undo_move(move);
1269 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1271 // Check for new best move
1272 if (value > bestValue)
1278 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1285 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1286 ttDepth, move, ss->staticEval, ss->evalMargin);
1294 // All legal moves have been searched. A special case: If we're in check
1295 // and no legal moves were found, it is checkmate.
1296 if (InCheck && bestValue == -VALUE_INFINITE)
1297 return mated_in(ss->ply); // Plies to mate from the root
1299 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1300 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1301 ttDepth, bestMove, ss->staticEval, ss->evalMargin);
1303 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1309 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1310 // "plies to mate from the current position". Non-mate scores are unchanged.
1311 // The function is called before storing a value to the transposition table.
1313 Value value_to_tt(Value v, int ply) {
1315 assert(v != VALUE_NONE);
1317 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1318 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1322 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1323 // from the transposition table (where refers to the plies to mate/be mated
1324 // from current position) to "plies to mate/be mated from the root".
1326 Value value_from_tt(Value v, int ply) {
1328 return v == VALUE_NONE ? VALUE_NONE
1329 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1330 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1334 // check_is_dangerous() tests if a checking move can be pruned in qsearch()
1336 bool check_is_dangerous(Position& pos, Move move, Value futilityBase, Value beta)
1338 Piece pc = pos.piece_moved(move);
1339 Square from = from_sq(move);
1340 Square to = to_sq(move);
1341 Color them = ~pos.side_to_move();
1342 Square ksq = pos.king_square(them);
1343 Bitboard enemies = pos.pieces(them);
1344 Bitboard kingAtt = pos.attacks_from<KING>(ksq);
1345 Bitboard occ = pos.pieces() ^ from ^ ksq;
1346 Bitboard oldAtt = pos.attacks_from(pc, from, occ);
1347 Bitboard newAtt = pos.attacks_from(pc, to, occ);
1349 // Checks which give opponent's king at most one escape square are dangerous
1350 if (!more_than_one(kingAtt & ~(enemies | newAtt | to)))
1353 // Queen contact check is very dangerous
1354 if (type_of(pc) == QUEEN && (kingAtt & to))
1357 // Creating new double threats with checks is dangerous
1358 Bitboard b = (enemies ^ ksq) & newAtt & ~oldAtt;
1361 // Note that here we generate illegal "double move"!
1362 if (futilityBase + PieceValue[EG][pos.piece_on(pop_lsb(&b))] >= beta)
1370 // allows_move() tests whether the move at previous ply (first) somehow makes a
1371 // second move possible, for instance if the moving piece is the same in both
1372 // moves. Normally the second move is the threat move (the best move returned
1373 // from a null search that fails low).
1375 bool allows_move(const Position& pos, Move first, Move second) {
1377 assert(is_ok(first));
1378 assert(is_ok(second));
1379 assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
1380 assert(color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
1382 Square m1from = from_sq(first);
1383 Square m2from = from_sq(second);
1384 Square m1to = to_sq(first);
1385 Square m2to = to_sq(second);
1387 // The piece is the same or second's destination was vacated by the first move
1388 if (m1to == m2from || m2to == m1from)
1391 // Second one moves through the square vacated by first one
1392 if (between_bb(m2from, m2to) & m1from)
1395 // Second's destination is defended by the first move's piece
1396 Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
1400 // Second move gives a discovered check through the first's checking piece
1401 if (m1att & pos.king_square(pos.side_to_move()))
1403 assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
1411 // prevents_move() tests whether a move (first) is able to defend against an
1412 // opponent's move (second). In this case will not be pruned. Normally the
1413 // second move is the threat move (the best move returned from a null search
1416 bool prevents_move(const Position& pos, Move first, Move second) {
1418 assert(is_ok(first));
1419 assert(is_ok(second));
1421 Square m1from = from_sq(first);
1422 Square m2from = from_sq(second);
1423 Square m1to = to_sq(first);
1424 Square m2to = to_sq(second);
1426 // Don't prune moves of the threatened piece
1430 // If the threatened piece has value less than or equal to the value of the
1431 // threat piece, don't prune moves which defend it.
1432 if ( pos.is_capture(second)
1433 && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
1434 || type_of(pos.piece_on(m2from)) == KING))
1436 // Update occupancy as if the piece and the threat are moving
1437 Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
1438 Piece piece = pos.piece_on(m1from);
1440 // The moved piece attacks the square 'tto' ?
1441 if (pos.attacks_from(piece, m1to, occ) & m2to)
1444 // Scan for possible X-ray attackers behind the moved piece
1445 Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(piece), QUEEN, ROOK))
1446 | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(piece), QUEEN, BISHOP));
1448 // Verify attackers are triggered by our move and not already existing
1449 if (xray && (xray ^ (xray & pos.attacks_from<QUEEN>(m2to))))
1453 // Don't prune safe moves which block the threat path
1454 if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
1461 // When playing with strength handicap choose best move among the MultiPV set
1462 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1464 Move Skill::pick_move() {
1468 // PRNG sequence should be not deterministic
1469 for (int i = Time::now() % 50; i > 0; i--)
1470 rk.rand<unsigned>();
1472 // RootMoves are already sorted by score in descending order
1473 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1474 int weakness = 120 - 2 * level;
1475 int max_s = -VALUE_INFINITE;
1478 // Choose best move. For each move score we add two terms both dependent on
1479 // weakness, one deterministic and bigger for weaker moves, and one random,
1480 // then we choose the move with the resulting highest score.
1481 for (size_t i = 0; i < PVSize; i++)
1483 int s = RootMoves[i].score;
1485 // Don't allow crazy blunders even at very low skills
1486 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1489 // This is our magic formula
1490 s += ( weakness * int(RootMoves[0].score - s)
1491 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1496 best = RootMoves[i].pv[0];
1503 // uci_pv() formats PV information according to UCI protocol. UCI requires
1504 // to send all the PV lines also if are still to be searched and so refer to
1505 // the previous search score.
1507 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1509 std::stringstream s;
1510 Time::point elaspsed = Time::now() - SearchTime + 1;
1511 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1514 for (size_t i = 0; i < Threads.size(); i++)
1515 if (Threads[i].maxPly > selDepth)
1516 selDepth = Threads[i].maxPly;
1518 for (size_t i = 0; i < uciPVSize; i++)
1520 bool updated = (i <= PVIdx);
1522 if (depth == 1 && !updated)
1525 int d = updated ? depth : depth - 1;
1526 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1528 if (s.rdbuf()->in_avail()) // Not at first line
1531 s << "info depth " << d
1532 << " seldepth " << selDepth
1533 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1534 << " nodes " << pos.nodes_searched()
1535 << " nps " << pos.nodes_searched() * 1000 / elaspsed
1536 << " time " << elaspsed
1537 << " multipv " << i + 1
1540 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1541 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1550 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1551 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1552 /// allow to always have a ponder move even when we fail high at root, and a
1553 /// long PV to print that is important for position analysis.
1555 void RootMove::extract_pv_from_tt(Position& pos) {
1557 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1567 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1569 pos.do_move(pv[ply++], *st++);
1570 tte = TT.probe(pos.key());
1573 && pos.is_pseudo_legal(m = tte->move()) // Local copy, TT could change
1574 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1576 && (!pos.is_draw<false>() || ply < 2));
1578 pv.push_back(MOVE_NONE); // Must be zero-terminating
1580 while (ply) pos.undo_move(pv[--ply]);
1584 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1585 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1586 /// first, even if the old TT entries have been overwritten.
1588 void RootMove::insert_pv_in_tt(Position& pos) {
1590 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1595 tte = TT.probe(pos.key());
1597 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1598 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE, VALUE_NONE);
1600 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1602 pos.do_move(pv[ply++], *st++);
1604 } while (pv[ply] != MOVE_NONE);
1606 while (ply) pos.undo_move(pv[--ply]);
1610 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1612 void Thread::idle_loop() {
1614 // Pointer 'this_sp' is not null only if we are called from split(), and not
1615 // at the thread creation. So it means we are the split point's master.
1616 const SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1618 assert(!this_sp || (this_sp->master == this && searching));
1620 // If this thread is the master of a split point and all slaves have finished
1621 // their work at this split point, return from the idle loop.
1622 while (!this_sp || this_sp->slavesMask)
1624 // If we are not searching, wait for a condition to be signaled instead of
1625 // wasting CPU time polling for work.
1626 while ((!searching && Threads.sleepWhileIdle) || exit)
1634 // Grab the lock to avoid races with Thread::notify_one()
1637 // If we are master and all slaves have finished then exit idle_loop
1638 if (this_sp && !this_sp->slavesMask)
1644 // Do sleep after retesting sleep conditions under lock protection, in
1645 // particular we need to avoid a deadlock in case a master thread has,
1646 // in the meanwhile, allocated us and sent the notify_one() call before
1647 // we had the chance to grab the lock.
1648 if (!searching && !exit)
1649 sleepCondition.wait(mutex);
1654 // If this thread has been assigned work, launch a search
1659 Threads.mutex.lock();
1662 SplitPoint* sp = activeSplitPoint;
1664 Threads.mutex.unlock();
1666 Stack ss[MAX_PLY_PLUS_2];
1667 Position pos(*sp->pos, this);
1669 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1674 assert(sp->slavesPositions[idx] == NULL);
1676 sp->slavesPositions[idx] = &pos;
1678 switch (sp->nodeType) {
1680 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1683 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1686 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1695 sp->slavesPositions[idx] = NULL;
1696 sp->slavesMask &= ~(1ULL << idx);
1697 sp->nodes += pos.nodes_searched();
1699 // Wake up master thread so to allow it to return from the idle loop
1700 // in case we are the last slave of the split point.
1701 if ( Threads.sleepWhileIdle
1702 && this != sp->master
1705 assert(!sp->master->searching);
1706 sp->master->notify_one();
1709 // After releasing the lock we cannot access anymore any SplitPoint
1710 // related data in a safe way becuase it could have been released under
1711 // our feet by the sp master. Also accessing other Thread objects is
1712 // unsafe because if we are exiting there is a chance are already freed.
1719 /// check_time() is called by the timer thread when the timer triggers. It is
1720 /// used to print debug info and, more important, to detect when we are out of
1721 /// available time and so stop the search.
1725 static Time::point lastInfoTime = Time::now();
1726 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1728 if (Time::now() - lastInfoTime >= 1000)
1730 lastInfoTime = Time::now();
1739 Threads.mutex.lock();
1741 nodes = RootPos.nodes_searched();
1743 // Loop across all split points and sum accumulated SplitPoint nodes plus
1744 // all the currently active slaves positions.
1745 for (size_t i = 0; i < Threads.size(); i++)
1746 for (int j = 0; j < Threads[i].splitPointsSize; j++)
1748 SplitPoint& sp = Threads[i].splitPoints[j];
1753 Bitboard sm = sp.slavesMask;
1756 Position* pos = sp.slavesPositions[pop_lsb(&sm)];
1757 nodes += pos ? pos->nodes_searched() : 0;
1763 Threads.mutex.unlock();
1766 Time::point elapsed = Time::now() - SearchTime;
1767 bool stillAtFirstMove = Signals.firstRootMove
1768 && !Signals.failedLowAtRoot
1769 && elapsed > TimeMgr.available_time();
1771 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1772 || stillAtFirstMove;
1774 if ( (Limits.use_time_management() && noMoreTime)
1775 || (Limits.movetime && elapsed >= Limits.movetime)
1776 || (Limits.nodes && nodes >= Limits.nodes))
1777 Signals.stop = true;