Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
- Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
// Different node types, used as a template parameter
enum NodeType { NonPV, PV };
- // Sizes and phases of the skip-blocks, used for distributing search depths across the threads
- constexpr int SkipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
- constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
-
// Razor and futility margins
- constexpr int RazorMargin = 600;
+ constexpr int RazorMargin = 661;
Value futility_margin(Depth d, bool improving) {
- return Value((175 - 50 * improving) * d / ONE_PLY);
+ return Value((168 - 51 * improving) * d / ONE_PLY);
}
- // Futility and reductions lookup tables, initialized at startup
- int FutilityMoveCounts[2][16]; // [improving][depth]
- int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
+ // Reductions lookup table, initialized at startup
+ int Reductions[MAX_MOVES]; // [depth or moveNumber]
+
+ Depth reduction(bool i, Depth d, int mn) {
+ int r = Reductions[d / ONE_PLY] * Reductions[mn];
+ return ((r + 520) / 1024 + (!i && r > 999)) * ONE_PLY;
+ }
- template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
- return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
+ constexpr int futility_move_count(bool improving, int depth) {
+ return (5 + depth * depth) * (1 + improving) / 2;
}
// History and stats update bonus, based on depth
int stat_bonus(Depth depth) {
int d = depth / ONE_PLY;
- return d > 17 ? 0 : 29 * d * d + 138 * d - 134;
+ return d > 17 ? -8 : 22 * d * d + 151 * d - 140;
}
- // Add a small random component to draw evaluations to keep search dynamic
- // and to avoid 3fold-blindness.
+ // Add a small random component to draw evaluations to avoid 3fold-blindness
Value value_draw(Depth depth, Thread* thisThread) {
- return depth < 4 ? VALUE_DRAW
- : VALUE_DRAW + Value(2 * (thisThread->nodes.load(std::memory_order_relaxed) % 2) - 1);
+ return depth < 4 * ONE_PLY ? VALUE_DRAW
+ : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
}
// Skill structure is used to implement strength limit
Move best = MOVE_NONE;
};
+ // Breadcrumbs are used to mark nodes as being searched by a given thread.
+ struct Breadcrumb {
+ std::atomic<Thread*> thread;
+ std::atomic<Key> key;
+ };
+ std::array<Breadcrumb, 1024> breadcrumbs;
+
+ // ThreadHolding keeps track of which thread left breadcrumbs at the given node for potential reductions.
+ // A free node will be marked upon entering the moves loop, and unmarked upon leaving that loop, by the ctor/dtor of this struct.
+ struct ThreadHolding {
+ explicit ThreadHolding(Thread* thisThread, Key posKey, int ply) {
+ location = ply < 8 ? &breadcrumbs[posKey & (breadcrumbs.size() - 1)] : nullptr;
+ otherThread = false;
+ owning = false;
+ if (location)
+ {
+ // see if another already marked this location, if not, mark it ourselves.
+ Thread* tmp = (*location).thread.load(std::memory_order_relaxed);
+ if (tmp == nullptr)
+ {
+ (*location).thread.store(thisThread, std::memory_order_relaxed);
+ (*location).key.store(posKey, std::memory_order_relaxed);
+ owning = true;
+ }
+ else if ( tmp != thisThread
+ && (*location).key.load(std::memory_order_relaxed) == posKey)
+ otherThread = true;
+ }
+ }
+
+ ~ThreadHolding() {
+ if (owning) // free the marked location.
+ (*location).thread.store(nullptr, std::memory_order_relaxed);
+ }
+
+ bool marked() { return otherThread; }
+
+ private:
+ Breadcrumb* location;
+ bool otherThread, owning;
+ };
+
template <NodeType NT>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
Value value_from_tt(Value v, int ply);
void update_pv(Move* pv, Move move, Move* childPv);
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
- void update_quiet_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
- void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCnt, int bonus);
-
- inline bool gives_check(const Position& pos, Move move) {
- Color us = pos.side_to_move();
- return type_of(move) == NORMAL && !(pos.blockers_for_king(~us) & pos.pieces(us))
- ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
- : pos.gives_check(move);
- }
+ void update_quiet_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietCount, int bonus);
+ void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCount, int bonus);
// perft() is our utility to verify move generation. All the leaf nodes up
// to the given depth are generated and counted, and the sum is returned.
void Search::init() {
- for (int imp = 0; imp <= 1; ++imp)
- for (int d = 1; d < 64; ++d)
- for (int mc = 1; mc < 64; ++mc)
- {
- double r = log(d) * log(mc) / 1.95;
-
- Reductions[NonPV][imp][d][mc] = int(std::round(r));
- Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
-
- // Increase reduction for non-PV nodes when eval is not improving
- if (!imp && r > 1.0)
- Reductions[NonPV][imp][d][mc]++;
- }
-
- for (int d = 0; d < 16; ++d)
- {
- FutilityMoveCounts[0][d] = int(2.4 + 0.74 * pow(d, 1.78));
- FutilityMoveCounts[1][d] = int(5.0 + 1.00 * pow(d, 2.00));
- }
+ for (int i = 1; i < MAX_MOVES; ++i)
+ Reductions[i] = int(23.4 * std::log(i));
}
Time.availableNodes = 0;
TT.clear();
Threads.clear();
+ Tablebases::init(Options["SyzygyPath"]); // Free mapped files
}
-/// MainThread::search() is called by the main thread when the program receives
-/// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
+/// MainThread::search() is started when the program receives the UCI 'go'
+/// command. It searches from the root position and outputs the "bestmove".
void MainThread::search() {
else
{
for (Thread* th : Threads)
+ {
+ th->bestMoveChanges = 0;
if (th != this)
th->start_searching();
+ }
Thread::search(); // Let's start searching!
}
// Threads.stop. However, if we are pondering or in an infinite search,
// the UCI protocol states that we shouldn't print the best move before the
// GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
- // until the GUI sends one of those commands (which also raises Threads.stop).
- Threads.stopOnPonderhit = true;
+ // until the GUI sends one of those commands.
- while (!Threads.stop && (Threads.ponder || Limits.infinite))
+ while (!Threads.stop && (ponder || Limits.infinite))
{} // Busy wait for a stop or a ponder reset
// Stop the threads if not already stopped (also raise the stop if
if (Limits.npmsec)
Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
- // Check if there are threads with a better score than main thread
Thread* bestThread = this;
+
+ // Check if there are threads with a better score than main thread
if ( Options["MultiPV"] == 1
&& !Limits.depth
- && !Skill(Options["Skill Level"]).enabled()
+ && !(Skill(Options["Skill Level"]).enabled() || Options["UCI_LimitStrength"])
&& rootMoves[0].pv[0] != MOVE_NONE)
{
- std::map<Move, int> votes;
+ std::map<Move, int64_t> votes;
Value minScore = this->rootMoves[0].score;
- // Find out minimum score and reset votes for moves which can be voted
+ // Find out minimum score
for (Thread* th: Threads)
- {
minScore = std::min(minScore, th->rootMoves[0].score);
- votes[th->rootMoves[0].pv[0]] = 0;
- }
- // Vote according to score and depth
- for (Thread* th : Threads)
- votes[th->rootMoves[0].pv[0]] += int(th->rootMoves[0].score - minScore)
- + int(th->completedDepth);
-
- // Select best thread
- int bestVote = votes[this->rootMoves[0].pv[0]];
+ // Vote according to score and depth, and select the best thread
for (Thread* th : Threads)
{
- if (votes[th->rootMoves[0].pv[0]] > bestVote)
+ votes[th->rootMoves[0].pv[0]] +=
+ (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
+
+ if (bestThread->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY)
{
- bestVote = votes[th->rootMoves[0].pv[0]];
- bestThread = th;
+ // Make sure we pick the shortest mate
+ if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
+ bestThread = th;
}
+ else if ( th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY
+ || votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]])
+ bestThread = th;
}
}
void Thread::search() {
- Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2)
+ // To allow access to (ss-7) up to (ss+2), the stack must be oversized.
+ // The former is needed to allow update_continuation_histories(ss-1, ...),
+ // which accesses its argument at ss-6, also near the root.
+ // The latter is needed for statScores and killer initialization.
+ Stack stack[MAX_PLY+10], *ss = stack+7;
+ Move pv[MAX_PLY+1];
Value bestValue, alpha, beta, delta;
Move lastBestMove = MOVE_NONE;
Depth lastBestMoveDepth = DEPTH_ZERO;
MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
- double timeReduction = 1.0;
+ double timeReduction = 1, totBestMoveChanges = 0;
Color us = rootPos.side_to_move();
- bool failedLow;
- std::memset(ss-4, 0, 7 * sizeof(Stack));
- for (int i = 4; i > 0; i--)
+ std::memset(ss-7, 0, 10 * sizeof(Stack));
+ for (int i = 7; i > 0; i--)
(ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel
+ ss->pv = pv;
bestValue = delta = alpha = -VALUE_INFINITE;
beta = VALUE_INFINITE;
- if (mainThread)
- mainThread->bestMoveChanges = 0, failedLow = false;
-
- size_t multiPV = Options["MultiPV"];
- Skill skill(Options["Skill Level"]);
+ multiPV = Options["MultiPV"];
+
+ // Pick integer skill levels, but non-deterministically round up or down
+ // such that the average integer skill corresponds to the input floating point one.
+ // UCI_Elo is converted to a suitable fractional skill level, using anchoring
+ // to CCRL Elo (goldfish 1.13 = 2000) and a fit through Ordo derived Elo
+ // for match (TC 60+0.6) results spanning a wide range of k values.
+ PRNG rng(now());
+ double floatLevel = Options["UCI_LimitStrength"] ?
+ clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) :
+ double(Options["Skill Level"]);
+ int intLevel = int(floatLevel) +
+ ((floatLevel - int(floatLevel)) * 1024 > rng.rand<unsigned>() % 1024 ? 1 : 0);
+ Skill skill(intLevel);
// When playing with strength handicap enable MultiPV search that we will
// use behind the scenes to retrieve a set of possible moves.
: Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct
: ct;
- // In evaluate.cpp the evaluation is from the white point of view
+ // Evaluation score is from the white point of view
contempt = (us == WHITE ? make_score(ct, ct / 2)
: -make_score(ct, ct / 2));
&& !Threads.stop
&& !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth))
{
- // Distribute search depths across the helper threads
- if (idx > 0)
- {
- int i = (idx - 1) % 20;
- if (((rootDepth / ONE_PLY + SkipPhase[i]) / SkipSize[i]) % 2)
- continue; // Retry with an incremented rootDepth
- }
-
// Age out PV variability metric
if (mainThread)
- mainThread->bestMoveChanges *= 0.517, failedLow = false;
+ totBestMoveChanges /= 2;
// Save the last iteration's scores before first PV line is searched and
// all the move scores except the (new) PV are set to -VALUE_INFINITE.
selDepth = 0;
// Reset aspiration window starting size
- if (rootDepth >= 5 * ONE_PLY)
+ if (rootDepth >= 4 * ONE_PLY)
{
Value previousScore = rootMoves[pvIdx].previousScore;
- delta = Value(20);
+ delta = Value(23);
alpha = std::max(previousScore - delta,-VALUE_INFINITE);
beta = std::min(previousScore + delta, VALUE_INFINITE);
// Adjust contempt based on root move's previousScore (dynamic contempt)
- int dct = ct + 88 * previousScore / (abs(previousScore) + 200);
+ int dct = ct + 86 * previousScore / (abs(previousScore) + 176);
contempt = (us == WHITE ? make_score(dct, dct / 2)
: -make_score(dct, dct / 2));
beta = (alpha + beta) / 2;
alpha = std::max(bestValue - delta, -VALUE_INFINITE);
+ failedHighCnt = 0;
if (mainThread)
- {
- failedHighCnt = 0;
- failedLow = true;
- Threads.stopOnPonderhit = false;
- }
+ mainThread->stopOnPonderhit = false;
}
else if (bestValue >= beta)
{
beta = std::min(bestValue + delta, VALUE_INFINITE);
- if (mainThread)
- ++failedHighCnt;
+ ++failedHighCnt;
}
else
break;
// Do we have time for the next iteration? Can we stop searching now?
if ( Limits.use_time_management()
&& !Threads.stop
- && !Threads.stopOnPonderhit)
- {
- const int F[] = { failedLow,
- bestValue - mainThread->previousScore };
-
- int improvingFactor = std::max(246, std::min(832, 306 + 119 * F[0] - 6 * F[1]));
+ && !mainThread->stopOnPonderhit)
+ {
+ double fallingEval = (354 + 10 * (mainThread->previousScore - bestValue)) / 692.0;
+ fallingEval = clamp(fallingEval, 0.5, 1.5);
- // If the bestMove is stable over several iterations, reduce time accordingly
- timeReduction = 1.0;
- for (int i : {3, 4, 5})
- if (lastBestMoveDepth * i < completedDepth)
- timeReduction *= 1.25;
+ // If the bestMove is stable over several iterations, reduce time accordingly
+ timeReduction = lastBestMoveDepth + 9 * ONE_PLY < completedDepth ? 1.97 : 0.98;
+ double reduction = (1.36 + mainThread->previousTimeReduction) / (2.29 * timeReduction);
- // Use part of the gained time from a previous stable move for the current move
- double bestMoveInstability = 1.0 + mainThread->bestMoveChanges;
- bestMoveInstability *= std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction;
+ // Use part of the gained time from a previous stable move for the current move
+ for (Thread* th : Threads)
+ {
+ totBestMoveChanges += th->bestMoveChanges;
+ th->bestMoveChanges = 0;
+ }
+ double bestMoveInstability = 1 + totBestMoveChanges / Threads.size();
- // Stop the search if we have only one legal move, or if available time elapsed
- if ( rootMoves.size() == 1
- || Time.elapsed() > Time.optimum() * bestMoveInstability * improvingFactor / 581)
- {
- // If we are allowed to ponder do not stop the search now but
- // keep pondering until the GUI sends "ponderhit" or "stop".
- if (Threads.ponder)
- Threads.stopOnPonderhit = true;
- else
- Threads.stop = true;
- }
+ // Stop the search if we have only one legal move, or if available time elapsed
+ if ( rootMoves.size() == 1
+ || Time.elapsed() > Time.optimum() * fallingEval * reduction * bestMoveInstability)
+ {
+ // If we are allowed to ponder do not stop the search now but
+ // keep pondering until the GUI sends "ponderhit" or "stop".
+ if (mainThread->ponder)
+ mainThread->stopOnPonderhit = true;
+ else
+ Threads.stop = true;
}
+ }
}
if (!mainThread)
Key posKey;
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
- Value bestValue, value, ttValue, eval, maxValue, pureStaticEval;
- bool ttHit, inCheck, givesCheck, improving;
- bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
+ Value bestValue, value, ttValue, eval, maxValue;
+ bool ttHit, ttPv, inCheck, givesCheck, improving, doLMR;
+ bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
Piece movedPiece;
- int moveCount, captureCount, quietCount;
+ int moveCount, captureCount, quietCount, singularLMR;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
inCheck = pos.checkers();
Color us = pos.side_to_move();
- moveCount = captureCount = quietCount = ss->moveCount = 0;
+ moveCount = captureCount = quietCount = singularLMR = ss->moveCount = 0;
bestValue = -VALUE_INFINITE;
maxValue = VALUE_INFINITE;
if ( Threads.stop.load(std::memory_order_relaxed)
|| pos.is_draw(ss->ply)
|| ss->ply >= MAX_PLY)
- return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos)
+ return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos)
: value_draw(depth, pos.this_thread());
// Step 3. Mate distance pruning. Even if we mate at the next move our score
assert(0 <= ss->ply && ss->ply < MAX_PLY);
(ss+1)->ply = ss->ply + 1;
- ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
+ (ss+1)->excludedMove = bestMove = MOVE_NONE;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
Square prevSq = to_sq((ss-1)->currentMove);
// starts with statScore = 0. Later grandchildren start with the last calculated
// statScore of the previous grandchild. This influences the reduction rules in
// LMR which are based on the statScore of parent position.
- (ss+2)->statScore = 0;
+ if (rootNode)
+ (ss + 4)->statScore = 0;
+ else
+ (ss + 2)->statScore = 0;
// Step 4. Transposition table lookup. We don't want the score of a partial
// search to overwrite a previous full search TT value, so we use a different
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
: ttHit ? tte->move() : MOVE_NONE;
+ ttPv = PvNode || (ttHit && tte->is_pv());
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
if (!pos.capture_or_promotion(ttMove))
update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
- // Extra penalty for a quiet TT move in previous ply when it gets refuted
- if ((ss-1)->moveCount == 1 && !pos.captured_piece())
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+ // Extra penalty for early quiet moves of the previous ply
+ if ((ss-1)->moveCount <= 2 && !pos.captured_piece())
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
}
// Penalty for a quiet ttMove that fails low
else if (!pos.capture_or_promotion(ttMove))
TB::ProbeState err;
TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err);
+ // Force check of time on the next occasion
+ if (thisThread == Threads.main())
+ static_cast<MainThread*>(thisThread)->callsCnt = 0;
+
if (err != TB::ProbeState::FAIL)
{
thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
if ( b == BOUND_EXACT
|| (b == BOUND_LOWER ? value >= beta : value <= alpha))
{
- tte->save(posKey, value_to_tt(value, ss->ply), b,
+ tte->save(posKey, value_to_tt(value, ss->ply), ttPv, b,
std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
MOVE_NONE, VALUE_NONE);
// Step 6. Static evaluation of the position
if (inCheck)
{
- ss->staticEval = eval = pureStaticEval = VALUE_NONE;
+ ss->staticEval = eval = VALUE_NONE;
improving = false;
goto moves_loop; // Skip early pruning when in check
}
else if (ttHit)
{
- // Never assume anything on values stored in TT
- ss->staticEval = eval = pureStaticEval = tte->eval();
+ // Never assume anything about values stored in TT
+ ss->staticEval = eval = tte->eval();
if (eval == VALUE_NONE)
- ss->staticEval = eval = pureStaticEval = evaluate(pos);
+ ss->staticEval = eval = evaluate(pos);
// Can ttValue be used as a better position evaluation?
if ( ttValue != VALUE_NONE
{
if ((ss-1)->currentMove != MOVE_NULL)
{
- int p = (ss-1)->statScore;
- int bonus = p > 0 ? (-p - 2500) / 512 :
- p < 0 ? (-p + 2500) / 512 : 0;
+ int bonus = -(ss-1)->statScore / 512;
- pureStaticEval = evaluate(pos);
- ss->staticEval = eval = pureStaticEval + bonus;
+ ss->staticEval = eval = evaluate(pos) + bonus;
}
else
- ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo;
+ ss->staticEval = eval = -(ss-1)->staticEval + 2 * Eval::Tempo;
- tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval);
+ tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
// Step 7. Razoring (~2 Elo)
- if ( depth < 2 * ONE_PLY
- && eval <= alpha - RazorMargin)
+ if ( !rootNode // The required rootNode PV handling is not available in qsearch
+ && depth < 2 * ONE_PLY
+ && eval <= alpha - RazorMargin)
return qsearch<NT>(pos, ss, alpha, beta);
improving = ss->staticEval >= (ss-2)->staticEval
|| (ss-2)->staticEval == VALUE_NONE;
// Step 8. Futility pruning: child node (~30 Elo)
- if ( !rootNode
+ if ( !PvNode
&& depth < 7 * ONE_PLY
&& eval - futility_margin(depth, improving) >= beta
&& eval < VALUE_KNOWN_WIN) // Do not return unproven wins
// Step 9. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 23200
+ && (ss-1)->statScore < 22661
&& eval >= beta
- && pureStaticEval >= beta - 36 * depth / ONE_PLY + 225
+ && ss->staticEval >= beta - 33 * depth / ONE_PLY + 299
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth and value
- Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY;
+ Depth R = ((835 + 70 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 185, 3)) * ONE_PLY;
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
nullValue = beta;
- if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 12 * ONE_PLY))
+ if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13 * ONE_PLY))
return nullValue;
assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
// Do verification search at high depths, with null move pruning disabled
// for us, until ply exceeds nmpMinPly.
- thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4;
+ thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / (4 * ONE_PLY);
thisThread->nmpColor = us;
Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
&& depth >= 5 * ONE_PLY
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
- Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE);
- MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory);
+ Value raisedBeta = std::min(beta + 191 - 46 * improving, VALUE_INFINITE);
+ MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory);
int probCutCount = 0;
while ( (move = mp.next_move()) != MOVE_NONE
- && probCutCount < 3)
+ && probCutCount < 2 + 2 * cutNode)
if (move != excludedMove && pos.legal(move))
{
probCutCount++;
pos.do_move(move, st);
// Perform a preliminary qsearch to verify that the move holds
- value = -qsearch<NonPV>(pos, ss+1, -rbeta, -rbeta+1);
+ value = -qsearch<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1);
- // If the qsearch held perform the regular search
- if (value >= rbeta)
- value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode);
+ // If the qsearch held, perform the regular search
+ if (value >= raisedBeta)
+ value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4 * ONE_PLY, !cutNode);
pos.undo_move(move);
- if (value >= rbeta)
+ if (value >= raisedBeta)
return value;
}
}
// Step 11. Internal iterative deepening (~2 Elo)
- if ( depth >= 8 * ONE_PLY
- && !ttMove)
+ if (depth >= 7 * ONE_PLY && !ttMove)
{
search<NT>(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode);
moves_loop: // When in check, search starts from here
- const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
+ const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
+ nullptr, (ss-4)->continuationHistory,
+ nullptr, (ss-6)->continuationHistory };
+
Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
contHist,
countermove,
ss->killers);
- value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
- skipQuiets = false;
+ value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
+ moveCountPruning = false;
ttCapture = ttMove && pos.capture_or_promotion(ttMove);
- pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT;
+
+ // Mark this node as being searched.
+ ThreadHolding th(thisThread, posKey, ss->ply);
// Step 12. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
- while ((move = mp.next_move(skipQuiets)) != MOVE_NONE)
+ while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
{
assert(is_ok(move));
sync_cout << "info depth " << depth / ONE_PLY
<< " currmove " << UCI::move(move, pos.is_chess960())
<< " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl;
+
+ // In MultiPV mode also skip moves which will be searched later as PV moves
+ if (rootNode && std::count(thisThread->rootMoves.begin() + thisThread->pvIdx + 1,
+ thisThread->rootMoves.begin() + thisThread->multiPV, move))
+ continue;
+
if (PvNode)
(ss+1)->pv = nullptr;
extension = DEPTH_ZERO;
captureOrPromotion = pos.capture_or_promotion(move);
movedPiece = pos.moved_piece(move);
- givesCheck = gives_check(pos, move);
-
- moveCountPruning = depth < 16 * ONE_PLY
- && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
+ givesCheck = pos.gives_check(move);
// Step 13. Extensions (~70 Elo)
// then that move is singular and should be extended. To verify this we do
// a reduced search on all the other moves but the ttMove and if the
// result is lower than ttValue minus a margin then we will extend the ttMove.
- if ( depth >= 8 * ONE_PLY
+ if ( depth >= 6 * ONE_PLY
&& move == ttMove
&& !rootNode
- && !excludedMove // Recursive singular search is not allowed
- && ttValue != VALUE_NONE
+ && !excludedMove // Avoid recursive singular search
+ /* && ttValue != VALUE_NONE Already implicit in the next condition */
+ && abs(ttValue) < VALUE_KNOWN_WIN
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY
&& pos.legal(move))
{
- Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
+ Value singularBeta = ttValue - 2 * depth / ONE_PLY;
+ Depth halfDepth = depth / (2 * ONE_PLY) * ONE_PLY; // ONE_PLY invariant
ss->excludedMove = move;
- value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
+ value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode);
ss->excludedMove = MOVE_NONE;
- if (value < rBeta)
+ if (value < singularBeta)
+ {
extension = ONE_PLY;
+ singularLMR++;
+
+ if (value < singularBeta - std::min(4 * depth / ONE_PLY, 36))
+ singularLMR++;
+ }
+
+ // Multi-cut pruning
+ // Our ttMove is assumed to fail high, and now we failed high also on a reduced
+ // search without the ttMove. So we assume this expected Cut-node is not singular,
+ // that multiple moves fail high, and we can prune the whole subtree by returning
+ // a soft bound.
+ else if ( eval >= beta
+ && singularBeta >= beta)
+ return singularBeta;
}
- else if ( givesCheck // Check extension (~2 Elo)
- && pos.see_ge(move))
+
+ // Check extension (~2 Elo)
+ else if ( givesCheck
+ && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move)))
extension = ONE_PLY;
- // Extension for king moves that change castling rights
- if ( pos.can_castle(us)
- && type_of(movedPiece) == KING
- && depth < 12 * ONE_PLY)
+ // Castling extension
+ else if (type_of(move) == CASTLING)
+ extension = ONE_PLY;
+
+ // Shuffle extension
+ else if ( PvNode
+ && pos.rule50_count() > 18
+ && depth < 3 * ONE_PLY
+ && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4) // To avoid too many extensions
+ extension = ONE_PLY;
+
+ // Passed pawn extension
+ else if ( move == ss->killers[0]
+ && pos.advanced_pawn_push(move)
+ && pos.pawn_passed(us, to_sq(move)))
extension = ONE_PLY;
// Calculate new depth for this move
&& pos.non_pawn_material(us)
&& bestValue > VALUE_MATED_IN_MAX_PLY)
{
+ // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
+ moveCountPruning = moveCount >= futility_move_count(improving, depth / ONE_PLY);
+
if ( !captureOrPromotion
&& !givesCheck
- && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000)))
+ && (!pos.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg))
{
- // Move count based pruning (~30 Elo)
+ // Move count based pruning
if (moveCountPruning)
- {
- skipQuiets = true;
continue;
- }
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
+ int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO);
+ lmrDepth /= ONE_PLY;
// Countermoves based pruning (~20 Elo)
- if ( lmrDepth < 3 + ((ss-1)->statScore > 0)
+ if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
continue;
// Futility pruning: parent node (~2 Elo)
- if ( lmrDepth < 7
+ if ( lmrDepth < 6
&& !inCheck
- && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
+ && ss->staticEval + 250 + 211 * lmrDepth <= alpha)
continue;
// Prune moves with negative SEE (~10 Elo)
- if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))
+ if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
- else if ( !extension // (~20 Elo)
- && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
+ else if ( (!givesCheck || !extension)
+ && !pos.see_ge(move, Value(-199) * (depth / ONE_PLY))) // (~20 Elo)
continue;
}
// Step 16. Reduced depth search (LMR). If the move fails high it will be
// re-searched at full depth.
if ( depth >= 3 * ONE_PLY
- && moveCount > 1
- && (!captureOrPromotion || moveCountPruning))
+ && moveCount > 1 + 3 * rootNode
+ && ( !captureOrPromotion
+ || moveCountPruning
+ || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha))
{
- Depth r = reduction<PvNode>(improving, depth, moveCount);
+ Depth r = reduction(improving, depth, moveCount);
+
+ // Reduction if other threads are searching this position.
+ if (th.marked())
+ r += ONE_PLY;
+
+ // Decrease reduction if position is or has been on the PV
+ if (ttPv)
+ r -= 2 * ONE_PLY;
// Decrease reduction if opponent's move count is high (~10 Elo)
if ((ss-1)->moveCount > 15)
r -= ONE_PLY;
+ // Decrease reduction if move has been singularly extended
+ r -= singularLMR * ONE_PLY;
+
if (!captureOrPromotion)
{
- // Decrease reduction for exact PV nodes (~0 Elo)
- if (pvExact)
- r -= ONE_PLY;
-
// Increase reduction if ttMove is a capture (~0 Elo)
if (ttCapture)
r += ONE_PLY;
+ (*contHist[0])[movedPiece][to_sq(move)]
+ (*contHist[1])[movedPiece][to_sq(move)]
+ (*contHist[3])[movedPiece][to_sq(move)]
- - 4000;
+ - 4729;
+
+ // Reset statScore to zero if negative and most stats shows >= 0
+ if ( ss->statScore < 0
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 0
+ && (*contHist[1])[movedPiece][to_sq(move)] >= 0
+ && thisThread->mainHistory[us][from_to(move)] >= 0)
+ ss->statScore = 0;
// Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= 0 && (ss-1)->statScore < 0)
+ if (ss->statScore >= -99 && (ss-1)->statScore < -116)
r -= ONE_PLY;
- else if ((ss-1)->statScore >= 0 && ss->statScore < 0)
+ else if ((ss-1)->statScore >= -117 && ss->statScore < -144)
r += ONE_PLY;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r -= ss->statScore / 20000 * ONE_PLY;
+ r -= ss->statScore / 16384 * ONE_PLY;
}
- Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY);
+ Depth d = clamp(newDepth - r, ONE_PLY, newDepth);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- doFullDepthSearch = (value > alpha && d != newDepth);
+ doFullDepthSearch = (value > alpha && d != newDepth), doLMR = true;
}
else
- doFullDepthSearch = !PvNode || moveCount > 1;
+ doFullDepthSearch = !PvNode || moveCount > 1, doLMR = false;
// Step 17. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
+ {
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+ if (doLMR && !captureOrPromotion)
+ {
+ int bonus = value > alpha ? stat_bonus(newDepth)
+ : -stat_bonus(newDepth);
+
+ if (move == ss->killers[0])
+ bonus += bonus / 4;
+
+ update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
+ }
+ }
+
// For PV nodes only, do a full PV search on the first move or after a fail
// high (in the latter case search only if value < beta), otherwise let the
// parent node fail low with value <= alpha and try another move.
// We record how often the best move has been changed in each
// iteration. This information is used for time management: When
// the best move changes frequently, we allocate some more time.
- if (moveCount > 1 && thisThread == Threads.main())
- ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
+ if (moveCount > 1)
+ ++thisThread->bestMoveChanges;
}
else
// All other moves but the PV are set to the lowest value: this
update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY));
- // Extra penalty for a quiet TT move in previous ply when it gets refuted
- if ((ss-1)->moveCount == 1 && !pos.captured_piece())
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+ // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
+ if ( ((ss-1)->moveCount == 1 || ((ss-1)->currentMove == (ss-1)->killers[0]))
+ && !pos.captured_piece())
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+
}
// Bonus for prior countermove that caused the fail low
else if ( (depth >= 3 * ONE_PLY || PvNode)
- && !pos.captured_piece()
- && is_ok((ss-1)->currentMove))
+ && !pos.captured_piece())
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
if (PvNode)
bestValue = std::min(bestValue, maxValue);
if (!excludedMove)
- tte->save(posKey, value_to_tt(bestValue, ss->ply),
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), ttPv,
bestValue >= beta ? BOUND_LOWER :
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
- depth, bestMove, pureStaticEval);
+ depth, bestMove, ss->staticEval);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
}
- // qsearch() is the quiescence search function, which is called by the main
- // search function with depth zero, or recursively with depth less than ONE_PLY.
+ // qsearch() is the quiescence search function, which is called by the main search
+ // function with zero depth, or recursively with further decreasing depth per call.
template <NodeType NT>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
Move ttMove, move, bestMove;
Depth ttDepth;
Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
- bool ttHit, inCheck, givesCheck, evasionPrunable;
+ bool ttHit, pvHit, inCheck, givesCheck, evasionPrunable;
int moveCount;
if (PvNode)
Thread* thisThread = pos.this_thread();
(ss+1)->ply = ss->ply + 1;
- ss->currentMove = bestMove = MOVE_NONE;
- ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
+ bestMove = MOVE_NONE;
inCheck = pos.checkers();
moveCount = 0;
tte = TT.probe(posKey, ttHit);
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
ttMove = ttHit ? tte->move() : MOVE_NONE;
+ pvHit = ttHit && tte->is_pv();
if ( !PvNode
&& ttHit
{
if (ttHit)
{
- // Never assume anything on values stored in TT
+ // Never assume anything about values stored in TT
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
ss->staticEval = bestValue = evaluate(pos);
if (bestValue >= beta)
{
if (!ttHit)
- tte->save(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER,
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, BOUND_LOWER,
DEPTH_NONE, MOVE_NONE, ss->staticEval);
return bestValue;
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 128;
+ futilityBase = bestValue + 153;
}
- const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
+ const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
+ nullptr, (ss-4)->continuationHistory,
+ nullptr, (ss-6)->continuationHistory };
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
{
assert(is_ok(move));
- givesCheck = gives_check(pos, move);
+ givesCheck = pos.gives_check(move);
moveCount++;
// Don't search moves with negative SEE values
if ( (!inCheck || evasionPrunable)
+ && (!givesCheck || !(pos.blockers_for_king(~pos.side_to_move()) & from_sq(move)))
&& !pos.see_ge(move))
continue;
if (value > alpha)
{
+ bestMove = move;
+
if (PvNode) // Update pv even in fail-high case
update_pv(ss->pv, move, (ss+1)->pv);
if (PvNode && value < beta) // Update alpha here!
- {
alpha = value;
- bestMove = move;
- }
- else // Fail high
- {
- tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
- ttDepth, move, ss->staticEval);
-
- return value;
- }
+ else
+ break; // Fail high
}
}
}
if (inCheck && bestValue == -VALUE_INFINITE)
return mated_in(ss->ply); // Plies to mate from the root
- tte->save(posKey, value_to_tt(bestValue, ss->ply),
- PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
+ bestValue >= beta ? BOUND_LOWER :
+ PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
ttDepth, bestMove, ss->staticEval);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
- for (int i : {1, 2, 4})
+ for (int i : {1, 2, 4, 6})
if (is_ok((ss-i)->currentMove))
(*(ss-i)->continuationHistory)[pc][to] << bonus;
}
// update_capture_stats() updates move sorting heuristics when a new capture best move is found
void update_capture_stats(const Position& pos, Move move,
- Move* captures, int captureCnt, int bonus) {
+ Move* captures, int captureCount, int bonus) {
- CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory;
+ CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory;
Piece moved_piece = pos.moved_piece(move);
PieceType captured = type_of(pos.piece_on(to_sq(move)));
captureHistory[moved_piece][to_sq(move)][captured] << bonus;
// Decrease all the other played capture moves
- for (int i = 0; i < captureCnt; ++i)
+ for (int i = 0; i < captureCount; ++i)
{
moved_piece = pos.moved_piece(captures[i]);
captured = type_of(pos.piece_on(to_sq(captures[i])));
// update_quiet_stats() updates move sorting heuristics when a new quiet best move is found
void update_quiet_stats(const Position& pos, Stack* ss, Move move,
- Move* quiets, int quietsCnt, int bonus) {
+ Move* quiets, int quietCount, int bonus) {
if (ss->killers[0] != move)
{
}
// Decrease all the other played quiet moves
- for (int i = 0; i < quietsCnt; ++i)
+ for (int i = 0; i < quietCount; ++i)
{
thisThread->mainHistory[us][from_to(quiets[i])] << -bonus;
update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
}
// We should not stop pondering until told so by the GUI
- if (Threads.ponder)
+ if (ponder)
return;
- if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
+ if ( (Limits.use_time_management() && (elapsed > Time.maximum() - 10 || stopOnPonderhit))
|| (Limits.movetime && elapsed >= Limits.movetime)
|| (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
Threads.stop = true;
assert(pv.size() == 1);
- if (!pv[0])
+ if (pv[0] == MOVE_NONE)
return false;
pos.do_move(pv[0], st);
}
else
{
- // Assign the same rank to all moves
+ // Clean up if root_probe() and root_probe_wdl() have failed
for (auto& m : rootMoves)
m.tbRank = 0;
}
projects / stockfish / blobdiff