2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
24 #include <cstring> // For std::memset
37 #include "syzygy/tbprobe.h"
45 namespace Tablebases {
55 namespace TB = Tablebases;
59 using namespace Search;
63 // Different node types, used as a template parameter
64 enum NodeType { NonPV, PV };
66 // Razoring and futility margin based on depth
67 const int razor_margin[4] = { 483, 570, 603, 554 };
68 Value futility_margin(Depth d) { return Value(150 * d); }
70 // Futility and reductions lookup tables, initialized at startup
71 int FutilityMoveCounts[2][16]; // [improving][depth]
72 Depth Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
74 template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
75 return Reductions[PvNode][i][std::min(d, 63 * ONE_PLY)][std::min(mn, 63)];
78 // Skill structure is used to implement strength limit
80 Skill(int l) : level(l) {}
81 bool enabled() const { return level < 20; }
82 bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
83 Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
84 Move pick_best(size_t multiPV);
87 Move best = MOVE_NONE;
90 // EasyMoveManager structure is used to detect an 'easy move'. When the PV is
91 // stable across multiple search iterations, we can quickly return the best move.
92 struct EasyMoveManager {
97 pv[0] = pv[1] = pv[2] = MOVE_NONE;
100 Move get(Key key) const {
101 return expectedPosKey == key ? pv[2] : MOVE_NONE;
104 void update(Position& pos, const std::vector<Move>& newPv) {
106 assert(newPv.size() >= 3);
108 // Keep track of how many times in a row the 3rd ply remains stable
109 stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
111 if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
113 std::copy(newPv.begin(), newPv.begin() + 3, pv);
116 pos.do_move(newPv[0], st[0], pos.gives_check(newPv[0], CheckInfo(pos)));
117 pos.do_move(newPv[1], st[1], pos.gives_check(newPv[1], CheckInfo(pos)));
118 expectedPosKey = pos.key();
119 pos.undo_move(newPv[1]);
120 pos.undo_move(newPv[0]);
129 // Set of rows with half bits set to 1 and half to 0. It is used to allocate
130 // the search depths across the threads.
131 typedef std::vector<int> Row;
133 const Row HalfDensity[] = {
146 {0, 0, 0, 0, 1, 1, 1, 1},
147 {0, 0, 0, 1, 1, 1, 1, 0},
148 {0, 0, 1, 1, 1, 1, 0 ,0},
149 {0, 1, 1, 1, 1, 0, 0 ,0},
150 {1, 1, 1, 1, 0, 0, 0 ,0},
151 {1, 1, 1, 0, 0, 0, 0 ,1},
152 {1, 1, 0, 0, 0, 0, 1 ,1},
153 {1, 0, 0, 0, 0, 1, 1 ,1},
156 const size_t HalfDensitySize = std::extent<decltype(HalfDensity)>::value;
158 EasyMoveManager EasyMove;
159 Value DrawValue[COLOR_NB];
160 CounterMoveHistoryStats CounterMoveHistory;
162 template <NodeType NT>
163 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
165 template <NodeType NT, bool InCheck>
166 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
168 Value value_to_tt(Value v, int ply);
169 Value value_from_tt(Value v, int ply);
170 void update_pv(Move* pv, Move move, Move* childPv);
171 void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, Value bonus);
172 void update_opponent_stats(const Position& pos, Stack* ss, Value bonus);
178 /// Search::init() is called during startup to initialize various lookup tables
180 void Search::init() {
182 for (int imp = 0; imp <= 1; ++imp)
183 for (int d = 1; d < 64; ++d)
184 for (int mc = 1; mc < 64; ++mc)
186 double r = log(d) * log(mc) / 2;
190 Reductions[NonPV][imp][d][mc] = int(std::round(r)) * ONE_PLY;
191 Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - ONE_PLY, DEPTH_ZERO);
193 // Increase reduction for non-PV nodes when eval is not improving
194 if (!imp && Reductions[NonPV][imp][d][mc] >= 2 * ONE_PLY)
195 Reductions[NonPV][imp][d][mc] += ONE_PLY;
198 for (int d = 0; d < 16; ++d)
200 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
201 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
206 /// Search::clear() resets search state to zero, to obtain reproducible results
208 void Search::clear() {
211 CounterMoveHistory.clear();
213 for (Thread* th : Threads)
216 th->counterMoves.clear();
220 Threads.main()->previousScore = VALUE_INFINITE;
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 is returned.
227 uint64_t Search::perft(Position& pos, Depth depth) {
230 uint64_t cnt, nodes = 0;
232 const bool leaf = (depth == 2 * ONE_PLY);
234 for (const auto& m : MoveList<LEGAL>(pos))
236 if (Root && depth <= ONE_PLY)
240 pos.do_move(m, st, pos.gives_check(m, ci));
241 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
246 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
251 template uint64_t Search::perft<true>(Position&, Depth);
254 /// MainThread::search() is called by the main thread when the program receives
255 /// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
257 void MainThread::search() {
259 Color us = rootPos.side_to_move();
260 Time.init(Limits, us, rootPos.game_ply());
262 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
263 DrawValue[ us] = VALUE_DRAW - Value(contempt);
264 DrawValue[~us] = VALUE_DRAW + Value(contempt);
266 if (rootMoves.empty())
268 rootMoves.push_back(RootMove(MOVE_NONE));
269 sync_cout << "info depth 0 score "
270 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
275 for (Thread* th : Threads)
277 th->start_searching();
279 Thread::search(); // Let's start searching!
282 // When playing in 'nodes as time' mode, subtract the searched nodes from
283 // the available ones before exiting.
285 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
287 // When we reach the maximum depth, we can arrive here without a raise of
288 // Signals.stop. However, if we are pondering or in an infinite search,
289 // the UCI protocol states that we shouldn't print the best move before the
290 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
291 // until the GUI sends one of those commands (which also raises Signals.stop).
292 if (!Signals.stop && (Limits.ponder || Limits.infinite))
294 Signals.stopOnPonderhit = true;
298 // Stop the threads if not already stopped
301 // Wait until all threads have finished
302 for (Thread* th : Threads)
304 th->wait_for_search_finished();
306 // Check if there are threads with a better score than main thread
307 Thread* bestThread = this;
308 if ( !this->easyMovePlayed
309 && Options["MultiPV"] == 1
311 && !Skill(Options["Skill Level"]).enabled()
312 && rootMoves[0].pv[0] != MOVE_NONE)
314 for (Thread* th : Threads)
315 if ( th->completedDepth > bestThread->completedDepth
316 && th->rootMoves[0].score > bestThread->rootMoves[0].score)
320 previousScore = bestThread->rootMoves[0].score;
322 // Send new PV when needed
323 if (bestThread != this)
324 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
326 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
328 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
329 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
331 std::cout << sync_endl;
335 // Thread::search() is the main iterative deepening loop. It calls search()
336 // repeatedly with increasing depth until the allocated thinking time has been
337 // consumed, the user stops the search, or the maximum search depth is reached.
339 void Thread::search() {
341 Stack stack[MAX_PLY+7], *ss = stack+5; // To allow referencing (ss-5) and (ss+2)
342 Value bestValue, alpha, beta, delta;
343 Move easyMove = MOVE_NONE;
344 MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
346 std::memset(ss-5, 0, 8 * sizeof(Stack));
348 bestValue = delta = alpha = -VALUE_INFINITE;
349 beta = VALUE_INFINITE;
350 completedDepth = DEPTH_ZERO;
354 easyMove = EasyMove.get(rootPos.key());
356 mainThread->easyMovePlayed = mainThread->failedLow = false;
357 mainThread->bestMoveChanges = 0;
361 size_t multiPV = Options["MultiPV"];
362 Skill skill(Options["Skill Level"]);
364 // When playing with strength handicap enable MultiPV search that we will
365 // use behind the scenes to retrieve a set of possible moves.
367 multiPV = std::max(multiPV, (size_t)4);
369 multiPV = std::min(multiPV, rootMoves.size());
371 // Iterative deepening loop until requested to stop or the target depth is reached.
372 while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || Threads.main()->rootDepth <= Limits.depth))
374 // Set up the new depths for the helper threads skipping on average every
375 // 2nd ply (using a half-density matrix).
378 const Row& row = HalfDensity[(idx - 1) % HalfDensitySize];
379 if (row[(rootDepth + rootPos.game_ply()) % row.size()])
383 // Age out PV variability metric
385 mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
387 // Save the last iteration's scores before first PV line is searched and
388 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
389 for (RootMove& rm : rootMoves)
390 rm.previousScore = rm.score;
392 // MultiPV loop. We perform a full root search for each PV line
393 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
395 // Reset aspiration window starting size
396 if (rootDepth >= 5 * ONE_PLY)
399 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
400 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
403 // Start with a small aspiration window and, in the case of a fail
404 // high/low, re-search with a bigger window until we're not failing
408 bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false);
410 // Bring the best move to the front. It is critical that sorting
411 // is done with a stable algorithm because all the values but the
412 // first and eventually the new best one are set to -VALUE_INFINITE
413 // and we want to keep the same order for all the moves except the
414 // new PV that goes to the front. Note that in case of MultiPV
415 // search the already searched PV lines are preserved.
416 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
418 // If search has been stopped, break immediately. Sorting and
419 // writing PV back to TT is safe because RootMoves is still
420 // valid, although it refers to the previous iteration.
424 // When failing high/low give some update (without cluttering
425 // the UI) before a re-search.
428 && (bestValue <= alpha || bestValue >= beta)
429 && Time.elapsed() > 3000)
430 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
432 // In case of failing low/high increase aspiration window and
433 // re-search, otherwise exit the loop.
434 if (bestValue <= alpha)
436 beta = (alpha + beta) / 2;
437 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
441 mainThread->failedLow = true;
442 Signals.stopOnPonderhit = false;
445 else if (bestValue >= beta)
447 alpha = (alpha + beta) / 2;
448 beta = std::min(bestValue + delta, VALUE_INFINITE);
453 delta += delta / 4 + 5;
455 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
458 // Sort the PV lines searched so far and update the GUI
459 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
465 sync_cout << "info nodes " << Threads.nodes_searched()
466 << " time " << Time.elapsed() << sync_endl;
468 else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
469 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
473 completedDepth = rootDepth;
478 // If skill level is enabled and time is up, pick a sub-optimal best move
479 if (skill.enabled() && skill.time_to_pick(rootDepth))
480 skill.pick_best(multiPV);
482 // Have we found a "mate in x"?
484 && bestValue >= VALUE_MATE_IN_MAX_PLY
485 && VALUE_MATE - bestValue <= 2 * Limits.mate)
488 // Do we have time for the next iteration? Can we stop searching now?
489 if (Limits.use_time_management())
491 if (!Signals.stop && !Signals.stopOnPonderhit)
493 // Stop the search if only one legal move is available, or if all
494 // of the available time has been used, or if we matched an easyMove
495 // from the previous search and just did a fast verification.
496 const int F[] = { mainThread->failedLow,
497 bestValue - mainThread->previousScore };
499 int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
500 double unstablePvFactor = 1 + mainThread->bestMoveChanges;
502 bool doEasyMove = rootMoves[0].pv[0] == easyMove
503 && mainThread->bestMoveChanges < 0.03
504 && Time.elapsed() > Time.optimum() * 5 / 42;
506 if ( rootMoves.size() == 1
507 || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
508 || (mainThread->easyMovePlayed = doEasyMove))
510 // If we are allowed to ponder do not stop the search now but
511 // keep pondering until the GUI sends "ponderhit" or "stop".
513 Signals.stopOnPonderhit = true;
519 if (rootMoves[0].pv.size() >= 3)
520 EasyMove.update(rootPos, rootMoves[0].pv);
529 // Clear any candidate easy move that wasn't stable for the last search
530 // iterations; the second condition prevents consecutive fast moves.
531 if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
534 // If skill level is enabled, swap best PV line with the sub-optimal one
536 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
537 rootMoves.end(), skill.best_move(multiPV)));
543 // search<>() is the main search function for both PV and non-PV nodes
545 template <NodeType NT>
546 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
548 const bool PvNode = NT == PV;
549 const bool rootNode = PvNode && (ss-1)->ply == 0;
551 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
552 assert(PvNode || (alpha == beta - 1));
553 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
554 assert(!(PvNode && cutNode));
556 Move pv[MAX_PLY+1], quietsSearched[64];
560 Move ttMove, move, excludedMove, bestMove;
561 Depth extension, newDepth, predictedDepth;
562 Value bestValue, value, ttValue, eval, nullValue;
563 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
564 bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
566 int moveCount, quietCount;
568 // Step 1. Initialize node
569 Thread* thisThread = pos.this_thread();
570 inCheck = pos.checkers();
571 moveCount = quietCount = ss->moveCount = 0;
572 bestValue = -VALUE_INFINITE;
573 ss->ply = (ss-1)->ply + 1;
575 // Check for the available remaining time
576 if (thisThread->resetCalls.load(std::memory_order_relaxed))
578 thisThread->resetCalls = false;
579 thisThread->callsCnt = 0;
581 if (++thisThread->callsCnt > 4096)
583 for (Thread* th : Threads)
584 th->resetCalls = true;
589 // Used to send selDepth info to GUI
590 if (PvNode && thisThread->maxPly < ss->ply)
591 thisThread->maxPly = ss->ply;
595 // Step 2. Check for aborted search and immediate draw
596 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY)
597 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
598 : DrawValue[pos.side_to_move()];
600 // Step 3. Mate distance pruning. Even if we mate at the next move our score
601 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
602 // a shorter mate was found upward in the tree then there is no need to search
603 // because we will never beat the current alpha. Same logic but with reversed
604 // signs applies also in the opposite condition of being mated instead of giving
605 // mate. In this case return a fail-high score.
606 alpha = std::max(mated_in(ss->ply), alpha);
607 beta = std::min(mate_in(ss->ply+1), beta);
612 assert(0 <= ss->ply && ss->ply < MAX_PLY);
614 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
615 ss->counterMoves = nullptr;
616 (ss+1)->skipEarlyPruning = false;
617 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
619 // Step 4. Transposition table lookup. We don't want the score of a partial
620 // search to overwrite a previous full search TT value, so we use a different
621 // position key in case of an excluded move.
622 excludedMove = ss->excludedMove;
623 posKey = excludedMove ? pos.exclusion_key() : pos.key();
624 tte = TT.probe(posKey, ttHit);
625 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
626 ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
627 : ttHit ? tte->move() : MOVE_NONE;
629 // At non-PV nodes we check for an early TT cutoff
632 && tte->depth() >= depth
633 && ttValue != VALUE_NONE // Possible in case of TT access race
634 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
635 : (tte->bound() & BOUND_UPPER)))
637 ss->currentMove = ttMove; // Can be MOVE_NONE
639 // If ttMove is quiet, update killers, history, counter move on TT hit
640 if (ttValue >= beta && ttMove)
642 int d = depth / ONE_PLY;
644 if (!pos.capture_or_promotion(ttMove))
646 Value bonus = Value(d * d + 2 * d - 2);
647 update_stats(pos, ss, ttMove, nullptr, 0, bonus);
650 // Extra penalty for a quiet TT move in previous ply when it gets refuted
651 if ((ss-1)->moveCount == 1 && !pos.captured_piece_type())
653 Value penalty = Value(d * d + 4 * d + 1);
654 update_opponent_stats(pos, ss, -penalty);
660 // Step 4a. Tablebase probe
661 if (!rootNode && TB::Cardinality)
663 int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
665 if ( piecesCnt <= TB::Cardinality
666 && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
667 && pos.rule50_count() == 0
668 && !pos.can_castle(ANY_CASTLING))
670 int found, v = Tablebases::probe_wdl(pos, &found);
676 int drawScore = TB::UseRule50 ? 1 : 0;
678 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
679 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
680 : VALUE_DRAW + 2 * v * drawScore;
682 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
683 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
684 MOVE_NONE, VALUE_NONE, TT.generation());
691 // Step 5. Evaluate the position statically
694 ss->staticEval = eval = VALUE_NONE;
700 // Never assume anything on values stored in TT
701 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
702 eval = ss->staticEval = evaluate(pos);
704 // Can ttValue be used as a better position evaluation?
705 if (ttValue != VALUE_NONE)
706 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
711 eval = ss->staticEval =
712 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
713 : -(ss-1)->staticEval + 2 * Eval::Tempo;
715 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
716 ss->staticEval, TT.generation());
719 if (ss->skipEarlyPruning)
722 // Step 6. Razoring (skipped when in check)
724 && depth < 4 * ONE_PLY
725 && eval + razor_margin[depth] <= alpha
726 && ttMove == MOVE_NONE)
728 if ( depth <= ONE_PLY
729 && eval + razor_margin[3 * ONE_PLY] <= alpha)
730 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
732 Value ralpha = alpha - razor_margin[depth];
733 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
738 // Step 7. Futility pruning: child node (skipped when in check)
740 && depth < 7 * ONE_PLY
741 && eval - futility_margin(depth) >= beta
742 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
743 && pos.non_pawn_material(pos.side_to_move()))
744 return eval - futility_margin(depth);
746 // Step 8. Null move search with verification search (is omitted in PV nodes)
749 && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
750 && pos.non_pawn_material(pos.side_to_move()))
752 ss->currentMove = MOVE_NULL;
753 ss->counterMoves = nullptr;
755 assert(eval - beta >= 0);
757 // Null move dynamic reduction based on depth and value
758 Depth R = ((823 + 67 * depth) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
760 pos.do_null_move(st);
761 (ss+1)->skipEarlyPruning = true;
762 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
763 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
764 (ss+1)->skipEarlyPruning = false;
765 pos.undo_null_move();
767 if (nullValue >= beta)
769 // Do not return unproven mate scores
770 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
773 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
776 // Do verification search at high depths
777 ss->skipEarlyPruning = true;
778 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
779 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
780 ss->skipEarlyPruning = false;
787 // Step 9. ProbCut (skipped when in check)
788 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
789 // and a reduced search returns a value much above beta, we can (almost)
790 // safely prune the previous move.
792 && depth >= 5 * ONE_PLY
793 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
795 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
796 Depth rdepth = depth - 4 * ONE_PLY;
798 assert(rdepth >= ONE_PLY);
799 assert((ss-1)->currentMove != MOVE_NONE);
800 assert((ss-1)->currentMove != MOVE_NULL);
802 MovePicker mp(pos, ttMove, PieceValue[MG][pos.captured_piece_type()]);
805 while ((move = mp.next_move()) != MOVE_NONE)
806 if (pos.legal(move, ci.pinned))
808 ss->currentMove = move;
809 ss->counterMoves = &CounterMoveHistory[pos.moved_piece(move)][to_sq(move)];
810 pos.do_move(move, st, pos.gives_check(move, ci));
811 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
818 // Step 10. Internal iterative deepening (skipped when in check)
819 if ( depth >= 6 * ONE_PLY
821 && (PvNode || ss->staticEval + 256 >= beta))
823 ss->skipEarlyPruning = true;
824 search<NT>(pos, ss, alpha, beta, 3 * depth / 4 - 2 * ONE_PLY, cutNode);
825 ss->skipEarlyPruning = false;
827 tte = TT.probe(posKey, ttHit);
828 ttMove = ttHit ? tte->move() : MOVE_NONE;
831 moves_loop: // When in check search starts from here
833 const CounterMoveStats* cmh = (ss-1)->counterMoves;
834 const CounterMoveStats* fmh = (ss-2)->counterMoves;
835 const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
837 MovePicker mp(pos, ttMove, depth, ss);
839 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
840 improving = ss->staticEval >= (ss-2)->staticEval
841 /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
842 ||(ss-2)->staticEval == VALUE_NONE;
844 singularExtensionNode = !rootNode
845 && depth >= 8 * ONE_PLY
846 && ttMove != MOVE_NONE
847 /* && ttValue != VALUE_NONE Already implicit in the next condition */
848 && abs(ttValue) < VALUE_KNOWN_WIN
849 && !excludedMove // Recursive singular search is not allowed
850 && (tte->bound() & BOUND_LOWER)
851 && tte->depth() >= depth - 3 * ONE_PLY;
853 // Step 11. Loop through moves
854 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
855 while ((move = mp.next_move()) != MOVE_NONE)
859 if (move == excludedMove)
862 // At root obey the "searchmoves" option and skip moves not listed in Root
863 // Move List. As a consequence any illegal move is also skipped. In MultiPV
864 // mode we also skip PV moves which have been already searched.
865 if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
866 thisThread->rootMoves.end(), move))
869 ss->moveCount = ++moveCount;
871 if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
872 sync_cout << "info depth " << depth / ONE_PLY
873 << " currmove " << UCI::move(move, pos.is_chess960())
874 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
877 (ss+1)->pv = nullptr;
879 extension = DEPTH_ZERO;
880 captureOrPromotion = pos.capture_or_promotion(move);
881 moved_piece = pos.moved_piece(move);
883 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
884 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
885 : pos.gives_check(move, ci);
887 moveCountPruning = depth < 16 * ONE_PLY
888 && moveCount >= FutilityMoveCounts[improving][depth];
890 // Step 12. Extend checks
893 && pos.see_sign(move) >= VALUE_ZERO)
896 // Singular extension search. If all moves but one fail low on a search of
897 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
898 // is singular and should be extended. To verify this we do a reduced search
899 // on all the other moves but the ttMove and if the result is lower than
900 // ttValue minus a margin then we extend the ttMove.
901 if ( singularExtensionNode
904 && pos.legal(move, ci.pinned))
906 Value rBeta = ttValue - 2 * depth / ONE_PLY;
907 ss->excludedMove = move;
908 ss->skipEarlyPruning = true;
909 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
910 ss->skipEarlyPruning = false;
911 ss->excludedMove = MOVE_NONE;
917 // Update the current move (this must be done after singular extension search)
918 newDepth = depth - ONE_PLY + extension;
920 // Step 13. Pruning at shallow depth
922 && !captureOrPromotion
925 && !pos.advanced_pawn_push(move)
926 && bestValue > VALUE_MATED_IN_MAX_PLY)
928 // Move count based pruning
929 if (moveCountPruning)
932 predictedDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO);
934 // Countermoves based pruning
935 if ( predictedDepth < 3 * ONE_PLY
936 && move != ss->killers[0]
937 && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
938 && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
939 && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh)))
942 // Futility pruning: parent node
943 if ( predictedDepth < 7 * ONE_PLY
944 && ss->staticEval + 256 + 200 * predictedDepth / ONE_PLY <= alpha)
947 // Prune moves with negative SEE at low depths and below a decreasing
948 // threshold at higher depths.
949 if (predictedDepth < 8 * ONE_PLY)
951 Value see_v = predictedDepth < 4 * ONE_PLY ? VALUE_ZERO
952 : -PawnValueMg * 2 * int(predictedDepth - 3 * ONE_PLY);
954 if (pos.see_sign(move) < see_v)
959 // Speculative prefetch as early as possible
960 prefetch(TT.first_entry(pos.key_after(move)));
962 // Check for legality just before making the move
963 if (!rootNode && !pos.legal(move, ci.pinned))
965 ss->moveCount = --moveCount;
969 ss->currentMove = move;
970 ss->counterMoves = &CounterMoveHistory[moved_piece][to_sq(move)];
972 // Step 14. Make the move
973 pos.do_move(move, st, givesCheck);
975 // Step 15. Reduced depth search (LMR). If the move fails high it will be
976 // re-searched at full depth.
977 if ( depth >= 3 * ONE_PLY
979 && (!captureOrPromotion || moveCountPruning))
981 Depth r = reduction<PvNode>(improving, depth, moveCount);
983 if (captureOrPromotion)
984 r -= r ? ONE_PLY : DEPTH_ZERO;
987 Value val = thisThread->history[moved_piece][to_sq(move)]
988 + (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
989 + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
990 + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
991 + thisThread->fromTo.get(~pos.side_to_move(), move);
993 // Increase reduction for cut nodes
997 // Decrease reduction for moves that escape a capture. Filter out
998 // castling moves, because they are coded as "king captures rook" and
999 // hence break make_move(). Also use see() instead of see_sign(),
1000 // because the destination square is empty.
1001 else if ( type_of(move) == NORMAL
1002 && type_of(pos.piece_on(to_sq(move))) != PAWN
1003 && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
1006 // Decrease/increase reduction for moves with a good/bad history
1007 int rHist = (val - 8000) / 20000;
1008 r = std::max(DEPTH_ZERO, r - rHist * ONE_PLY);
1011 Depth d = std::max(newDepth - r, ONE_PLY);
1013 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
1015 doFullDepthSearch = (value > alpha && d != newDepth);
1018 doFullDepthSearch = !PvNode || moveCount > 1;
1020 // Step 16. Full depth search when LMR is skipped or fails high
1021 if (doFullDepthSearch)
1022 value = newDepth < ONE_PLY ?
1023 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1024 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1025 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
1027 // For PV nodes only, do a full PV search on the first move or after a fail
1028 // high (in the latter case search only if value < beta), otherwise let the
1029 // parent node fail low with value <= alpha and try another move.
1030 if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
1033 (ss+1)->pv[0] = MOVE_NONE;
1035 value = newDepth < ONE_PLY ?
1036 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1037 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1038 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
1041 // Step 17. Undo move
1042 pos.undo_move(move);
1044 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1046 // Step 18. Check for a new best move
1047 // Finished searching the move. If a stop occurred, the return value of
1048 // the search cannot be trusted, and we return immediately without
1049 // updating best move, PV and TT.
1050 if (Signals.stop.load(std::memory_order_relaxed))
1055 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1056 thisThread->rootMoves.end(), move);
1058 // PV move or new best move ?
1059 if (moveCount == 1 || value > alpha)
1066 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1067 rm.pv.push_back(*m);
1069 // We record how often the best move has been changed in each
1070 // iteration. This information is used for time management: When
1071 // the best move changes frequently, we allocate some more time.
1072 if (moveCount > 1 && thisThread == Threads.main())
1073 ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
1076 // All other moves but the PV are set to the lowest value: this is
1077 // not a problem when sorting because the sort is stable and the
1078 // move position in the list is preserved - just the PV is pushed up.
1079 rm.score = -VALUE_INFINITE;
1082 if (value > bestValue)
1088 // If there is an easy move for this position, clear it if unstable
1090 && thisThread == Threads.main()
1091 && EasyMove.get(pos.key())
1092 && (move != EasyMove.get(pos.key()) || moveCount > 1))
1097 if (PvNode && !rootNode) // Update pv even in fail-high case
1098 update_pv(ss->pv, move, (ss+1)->pv);
1100 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1104 assert(value >= beta); // Fail high
1110 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1111 quietsSearched[quietCount++] = move;
1114 // The following condition would detect a stop only after move loop has been
1115 // completed. But in this case bestValue is valid because we have fully
1116 // searched our subtree, and we can anyhow save the result in TT.
1122 // Step 20. Check for mate and stalemate
1123 // All legal moves have been searched and if there are no legal moves, it
1124 // must be a mate or a stalemate. If we are in a singular extension search then
1125 // return a fail low score.
1127 bestValue = excludedMove ? alpha
1128 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1131 int d = depth / ONE_PLY;
1133 // Quiet best move: update killers, history and countermoves
1134 if (!pos.capture_or_promotion(bestMove))
1136 Value bonus = Value(d * d + 2 * d - 2);
1137 update_stats(pos, ss, bestMove, quietsSearched, quietCount, bonus);
1140 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1141 if ((ss-1)->moveCount == 1 && !pos.captured_piece_type())
1143 Value penalty = Value(d * d + 4 * d + 1);
1144 update_opponent_stats(pos, ss, -penalty);
1147 // Bonus for prior countermove that caused the fail low
1148 else if ( depth >= 3 * ONE_PLY
1149 && !pos.captured_piece_type()
1150 && is_ok((ss-1)->currentMove))
1152 int d = depth / ONE_PLY;
1153 Value bonus = Value(d * d + 2 * d - 2);
1154 update_opponent_stats(pos, ss, bonus);
1157 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1158 bestValue >= beta ? BOUND_LOWER :
1159 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1160 depth, bestMove, ss->staticEval, TT.generation());
1162 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1168 // qsearch() is the quiescence search function, which is called by the main
1169 // search function when the remaining depth is zero (or, to be more precise,
1170 // less than ONE_PLY).
1172 template <NodeType NT, bool InCheck>
1173 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1175 const bool PvNode = NT == PV;
1177 assert(InCheck == !!pos.checkers());
1178 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1179 assert(PvNode || (alpha == beta - 1));
1180 assert(depth <= DEPTH_ZERO);
1186 Move ttMove, move, bestMove;
1187 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1188 bool ttHit, givesCheck, evasionPrunable;
1193 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1195 ss->pv[0] = MOVE_NONE;
1198 ss->currentMove = bestMove = MOVE_NONE;
1199 ss->ply = (ss-1)->ply + 1;
1201 // Check for an instant draw or if the maximum ply has been reached
1202 if (pos.is_draw() || ss->ply >= MAX_PLY)
1203 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1204 : DrawValue[pos.side_to_move()];
1206 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1208 // Decide whether or not to include checks: this fixes also the type of
1209 // TT entry depth that we are going to use. Note that in qsearch we use
1210 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1211 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1212 : DEPTH_QS_NO_CHECKS;
1214 // Transposition table lookup
1216 tte = TT.probe(posKey, ttHit);
1217 ttMove = ttHit ? tte->move() : MOVE_NONE;
1218 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1222 && tte->depth() >= ttDepth
1223 && ttValue != VALUE_NONE // Only in case of TT access race
1224 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1225 : (tte->bound() & BOUND_UPPER)))
1227 ss->currentMove = ttMove; // Can be MOVE_NONE
1231 // Evaluate the position statically
1234 ss->staticEval = VALUE_NONE;
1235 bestValue = futilityBase = -VALUE_INFINITE;
1241 // Never assume anything on values stored in TT
1242 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1243 ss->staticEval = bestValue = evaluate(pos);
1245 // Can ttValue be used as a better position evaluation?
1246 if (ttValue != VALUE_NONE)
1247 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1248 bestValue = ttValue;
1251 ss->staticEval = bestValue =
1252 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1253 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1255 // Stand pat. Return immediately if static value is at least beta
1256 if (bestValue >= beta)
1259 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1260 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1265 if (PvNode && bestValue > alpha)
1268 futilityBase = bestValue + 128;
1271 // Initialize a MovePicker object for the current position, and prepare
1272 // to search the moves. Because the depth is <= 0 here, only captures,
1273 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1275 MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove));
1278 // Loop through the moves until no moves remain or a beta cutoff occurs
1279 while ((move = mp.next_move()) != MOVE_NONE)
1281 assert(is_ok(move));
1283 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1284 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1285 : pos.gives_check(move, ci);
1290 && futilityBase > -VALUE_KNOWN_WIN
1291 && !pos.advanced_pawn_push(move))
1293 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1295 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1297 if (futilityValue <= alpha)
1299 bestValue = std::max(bestValue, futilityValue);
1303 if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO)
1305 bestValue = std::max(bestValue, futilityBase);
1310 // Detect non-capture evasions that are candidates to be pruned
1311 evasionPrunable = InCheck
1312 && bestValue > VALUE_MATED_IN_MAX_PLY
1313 && !pos.capture(move);
1315 // Don't search moves with negative SEE values
1316 if ( (!InCheck || evasionPrunable)
1317 && type_of(move) != PROMOTION
1318 && pos.see_sign(move) < VALUE_ZERO)
1321 // Speculative prefetch as early as possible
1322 prefetch(TT.first_entry(pos.key_after(move)));
1324 // Check for legality just before making the move
1325 if (!pos.legal(move, ci.pinned))
1328 ss->currentMove = move;
1330 // Make and search the move
1331 pos.do_move(move, st, givesCheck);
1332 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1333 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1334 pos.undo_move(move);
1336 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1338 // Check for a new best move
1339 if (value > bestValue)
1345 if (PvNode) // Update pv even in fail-high case
1346 update_pv(ss->pv, move, (ss+1)->pv);
1348 if (PvNode && value < beta) // Update alpha here!
1355 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1356 ttDepth, move, ss->staticEval, TT.generation());
1364 // All legal moves have been searched. A special case: If we're in check
1365 // and no legal moves were found, it is checkmate.
1366 if (InCheck && bestValue == -VALUE_INFINITE)
1367 return mated_in(ss->ply); // Plies to mate from the root
1369 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1370 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1371 ttDepth, bestMove, ss->staticEval, TT.generation());
1373 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1379 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1380 // "plies to mate from the current position". Non-mate scores are unchanged.
1381 // The function is called before storing a value in the transposition table.
1383 Value value_to_tt(Value v, int ply) {
1385 assert(v != VALUE_NONE);
1387 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1388 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1392 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1393 // from the transposition table (which refers to the plies to mate/be mated
1394 // from current position) to "plies to mate/be mated from the root".
1396 Value value_from_tt(Value v, int ply) {
1398 return v == VALUE_NONE ? VALUE_NONE
1399 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1400 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1404 // update_pv() adds current move and appends child pv[]
1406 void update_pv(Move* pv, Move move, Move* childPv) {
1408 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1414 // update_opponent_stats() updates countermoves for prior opponent move, i.e.
1415 // (ss-1)->currentMove. Called for both capture and non-capture moves.
1417 void update_opponent_stats(const Position& pos, Stack* ss, Value bonus) {
1419 Square prevSq = to_sq((ss-1)->currentMove);
1421 CounterMoveStats* cmh = (ss-2)->counterMoves;
1422 CounterMoveStats* fmh1 = (ss-3)->counterMoves;
1423 CounterMoveStats* fmh2 = (ss-5)->counterMoves;
1426 cmh->update(pos.piece_on(prevSq), prevSq, bonus);
1429 fmh1->update(pos.piece_on(prevSq), prevSq, bonus);
1432 fmh2->update(pos.piece_on(prevSq), prevSq, bonus);
1436 // update_stats() updates killers, history, countermove and countermove plus
1437 // follow-up move history when a new quiet best move is found.
1439 void update_stats(const Position& pos, Stack* ss, Move move,
1440 Move* quiets, int quietsCnt, Value bonus) {
1442 if (ss->killers[0] != move)
1444 ss->killers[1] = ss->killers[0];
1445 ss->killers[0] = move;
1448 CounterMoveStats* cmh = (ss-1)->counterMoves;
1449 CounterMoveStats* fmh1 = (ss-2)->counterMoves;
1450 CounterMoveStats* fmh2 = (ss-4)->counterMoves;
1452 Color c = pos.side_to_move();
1453 Thread* thisThread = pos.this_thread();
1454 thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
1455 thisThread->fromTo.update(c, move, bonus);
1459 Square prevSq = to_sq((ss-1)->currentMove);
1460 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1461 cmh->update(pos.moved_piece(move), to_sq(move), bonus);
1465 fmh1->update(pos.moved_piece(move), to_sq(move), bonus);
1468 fmh2->update(pos.moved_piece(move), to_sq(move), bonus);
1470 // Decrease all the other played quiet moves
1471 for (int i = 0; i < quietsCnt; ++i)
1473 thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1474 thisThread->fromTo.update(c, quiets[i], -bonus);
1477 cmh->update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1480 fmh1->update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1483 fmh2->update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1488 // When playing with strength handicap, choose best move among a set of RootMoves
1489 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1491 Move Skill::pick_best(size_t multiPV) {
1493 const RootMoves& rootMoves = Threads.main()->rootMoves;
1494 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1496 // RootMoves are already sorted by score in descending order
1497 Value topScore = rootMoves[0].score;
1498 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1499 int weakness = 120 - 2 * level;
1500 int maxScore = -VALUE_INFINITE;
1502 // Choose best move. For each move score we add two terms, both dependent on
1503 // weakness. One is deterministic and bigger for weaker levels, and one is
1504 // random. Then we choose the move with the resulting highest score.
1505 for (size_t i = 0; i < multiPV; ++i)
1507 // This is our magic formula
1508 int push = ( weakness * int(topScore - rootMoves[i].score)
1509 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1511 if (rootMoves[i].score + push > maxScore)
1513 maxScore = rootMoves[i].score + push;
1514 best = rootMoves[i].pv[0];
1522 // check_time() is used to print debug info and, more importantly, to detect
1523 // when we are out of available time and thus stop the search.
1527 static TimePoint lastInfoTime = now();
1529 int elapsed = Time.elapsed();
1530 TimePoint tick = Limits.startTime + elapsed;
1532 if (tick - lastInfoTime >= 1000)
1534 lastInfoTime = tick;
1538 // An engine may not stop pondering until told so by the GUI
1542 if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
1543 || (Limits.movetime && elapsed >= Limits.movetime)
1544 || (Limits.nodes && Threads.nodes_searched() >= Limits.nodes))
1545 Signals.stop = true;
1551 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1552 /// that all (if any) unsearched PV lines are sent using a previous search score.
1554 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1556 std::stringstream ss;
1557 int elapsed = Time.elapsed() + 1;
1558 const RootMoves& rootMoves = pos.this_thread()->rootMoves;
1559 size_t PVIdx = pos.this_thread()->PVIdx;
1560 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1561 uint64_t nodes_searched = Threads.nodes_searched();
1563 for (size_t i = 0; i < multiPV; ++i)
1565 bool updated = (i <= PVIdx);
1567 if (depth == ONE_PLY && !updated)
1570 Depth d = updated ? depth : depth - ONE_PLY;
1571 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1573 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1574 v = tb ? TB::Score : v;
1576 if (ss.rdbuf()->in_avail()) // Not at first line
1580 << " depth " << d / ONE_PLY
1581 << " seldepth " << pos.this_thread()->maxPly
1582 << " multipv " << i + 1
1583 << " score " << UCI::value(v);
1585 if (!tb && i == PVIdx)
1586 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1588 ss << " nodes " << nodes_searched
1589 << " nps " << nodes_searched * 1000 / elapsed;
1591 if (elapsed > 1000) // Earlier makes little sense
1592 ss << " hashfull " << TT.hashfull();
1594 ss << " tbhits " << TB::Hits
1595 << " time " << elapsed
1598 for (Move m : rootMoves[i].pv)
1599 ss << " " << UCI::move(m, pos.is_chess960());
1606 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1607 /// before exiting the search, for instance, in case we stop the search during a
1608 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1609 /// otherwise in case of 'ponder on' we have nothing to think on.
1611 bool RootMove::extract_ponder_from_tt(Position& pos)
1616 assert(pv.size() == 1);
1618 pos.do_move(pv[0], st, pos.gives_check(pv[0], CheckInfo(pos)));
1619 TTEntry* tte = TT.probe(pos.key(), ttHit);
1623 Move m = tte->move(); // Local copy to be SMP safe
1624 if (MoveList<LEGAL>(pos).contains(m))
1628 pos.undo_move(pv[0]);
1629 return pv.size() > 1;
1632 void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
1636 UseRule50 = Options["Syzygy50MoveRule"];
1637 ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
1638 Cardinality = Options["SyzygyProbeLimit"];
1640 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
1641 if (Cardinality > MaxCardinality)
1643 Cardinality = MaxCardinality;
1644 ProbeDepth = DEPTH_ZERO;
1647 if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
1650 // If the current root position is in the tablebases, then RootMoves
1651 // contains only moves that preserve the draw or the win.
1652 RootInTB = root_probe(pos, rootMoves, TB::Score);
1655 Cardinality = 0; // Do not probe tablebases during the search
1657 else // If DTZ tables are missing, use WDL tables as a fallback
1659 // Filter out moves that do not preserve the draw or the win.
1660 RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
1662 // Only probe during search if winning
1663 if (TB::Score <= VALUE_DRAW)
1669 Hits = rootMoves.size();
1672 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
1673 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1