enum NodeType { NonPV, PV };
// 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(198 * (d / ONE_PLY - improving));
}
// Reductions lookup table, initialized at startup
int Reductions[MAX_MOVES]; // [depth or moveNumber]
- template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
- int r = Reductions[d / ONE_PLY] * Reductions[mn] / 1024;
- return ((r + 512) / 1024 + (!i && r > 1024) - PvNode) * ONE_PLY;
+ 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;
}
constexpr int futility_move_count(bool improving, int depth) {
// 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 avoid 3fold-blindness
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 structure 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 by the constructor, and unmarked upon leaving that loop by the destructor.
+ 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);
void Search::init() {
for (int i = 1; i < MAX_MOVES; ++i)
- Reductions[i] = int(1024 * std::log(i) / std::sqrt(1.95));
+ Reductions[i] = int(23.4 * std::log(i));
}
// 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, 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);
- // Vote according to score and depth
+ // Vote according to score and depth, and select the best thread
for (Thread* th : Threads)
{
- int64_t s = th->rootMoves[0].score - minScore + 1;
- votes[th->rootMoves[0].pv[0]] += 200 + s * s * int(th->completedDepth);
- }
+ votes[th->rootMoves[0].pv[0]] +=
+ (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
- // Select best thread
- auto bestVote = votes[this->rootMoves[0].pv[0]];
- for (Thread* th : Threads)
- if (votes[th->rootMoves[0].pv[0]] > bestVote)
+ 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;
+ }
}
previousScore = bestThread->rootMoves[0].score;
beta = VALUE_INFINITE;
size_t multiPV = Options["MultiPV"];
- Skill skill(Options["Skill Level"]);
+
+ // 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.
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;
mainThread->stopOnPonderhit = false;
- }
}
else if (bestValue >= beta)
{
beta = std::min(bestValue + delta, VALUE_INFINITE);
- if (mainThread)
- ++failedHighCnt;
+ ++failedHighCnt;
}
else
+ {
+ ++rootMoves[pvIdx].bestMoveCount;
break;
+ }
delta += delta / 4 + 5;
&& !Threads.stop
&& !mainThread->stopOnPonderhit)
{
- double fallingEval = (314 + 9 * (mainThread->previousScore - bestValue)) / 581.0;
+ 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 = lastBestMoveDepth + 10 * ONE_PLY < completedDepth ? 1.95 : 1.0;
- double reduction = std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction;
+ 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
for (Thread* th : Threads)
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
Value bestValue, value, ttValue, eval, maxValue;
- bool ttHit, ttPv, inCheck, givesCheck, improving;
+ 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;
// 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.
- if (rootNode)
- (ss + 4)->statScore = 0;
- else
- (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 = (ttHit && tte->is_pv()) || (PvNode && depth > 4 * ONE_PLY);
+ ttPv = PvNode || (ttHit && tte->is_pv());
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
// 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));
+ 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))
}
else if (ttHit)
{
- // Never assume anything on values stored in TT
+ // Never assume anything about values stored in TT
ss->staticEval = eval = tte->eval();
if (eval == VALUE_NONE)
ss->staticEval = eval = evaluate(pos);
// 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
- && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
+ && eval >= ss->staticEval
+ && ss->staticEval >= beta - 33 * depth / ONE_PLY + 299 - improving * 30
&& !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
&& depth >= 5 * ONE_PLY
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
- Value raisedBeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE);
+ Value raisedBeta = std::min(beta + 191 - 46 * improving, VALUE_INFINITE);
MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory);
int probCutCount = 0;
}
// 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);
moveCountPruning = false;
ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+ // 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(moveCountPruning)) != MOVE_NONE)
// 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 // Avoid recursive singular search
ss->excludedMove = MOVE_NONE;
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 is multiple moves fail high, and we can prune the whole subtree by returning
- // the hard beta bound.
- else if (cutNode && singularBeta > beta)
- return beta;
+ // 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;
}
// Check extension (~2 Elo)
else if ( givesCheck
- && (pos.blockers_for_king(~us) & from_sq(move) || pos.see_ge(move)))
+ && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move)))
extension = ONE_PLY;
// Castling extension
else if ( PvNode
&& pos.rule50_count() > 18
&& depth < 3 * ONE_PLY
- && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid too deep searches
+ && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4) // To avoid too many extensions
extension = ONE_PLY;
// Passed pawn extension
if ( !captureOrPromotion
&& !givesCheck
- && !pos.advanced_pawn_push(move))
+ && (!pos.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg))
{
- // Move count based pruning (~30 Elo)
+ // Move count based pruning
if (moveCountPruning)
continue;
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO);
+ 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 || (ss-1)->moveCount == 1)
+ 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 (!pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo)
+ 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
+ && moveCount > 1 + 2 * rootNode
+ && (!rootNode || thisThread->best_move_count(move) == 0)
&& ( !captureOrPromotion
|| moveCountPruning
- || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha))
+ || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
+ || cutNode))
{
- 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 -= ONE_PLY;
+ 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)
{
// Increase reduction if ttMove is a capture (~0 Elo)
// castling moves, because they are coded as "king captures rook" and
// hence break make_move(). (~5 Elo)
else if ( type_of(move) == NORMAL
- && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
+ && !pos.see_ge(reverse_move(move)))
r -= 2 * ONE_PLY;
ss->statScore = thisThread->mainHistory[us][from_to(move)]
+ (*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.
{
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 (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 128;
+ futilityBase = bestValue + 153;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
// 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;
void update_capture_stats(const Position& pos, Move move,
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)));
thisThread->mainHistory[us][from_to(move)] << bonus;
update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
+ if (type_of(pos.moved_piece(move)) != PAWN)
+ thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus;
+
if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
}
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