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) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2015-2020 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
constexpr uint64_t ttHitAverageResolution = 1024;
// Razor and futility margins
- constexpr int RazorMargin = 661;
+ constexpr int RazorMargin = 531;
Value futility_margin(Depth d, bool improving) {
- return Value(198 * (d - improving));
+ return Value(217 * (d - improving));
}
// Reductions lookup table, initialized at startup
Depth reduction(bool i, Depth d, int mn) {
int r = Reductions[d] * Reductions[mn];
- return (r + 520) / 1024 + (!i && r > 999);
+ return (r + 511) / 1024 + (!i && r > 1007);
}
constexpr int futility_move_count(bool improving, Depth depth) {
// History and stats update bonus, based on depth
int stat_bonus(Depth d) {
- return d > 17 ? -8 : 22 * d * d + 151 * d - 140;
+ return d > 15 ? -8 : 19 * d * d + 155 * d - 132;
}
// Add a small random component to draw evaluations to avoid 3fold-blindness
void Search::init() {
for (int i = 1; i < MAX_MOVES; ++i)
- Reductions[i] = int((23.4 + std::log(Threads.size()) / 2) * std::log(i));
+ Reductions[i] = int((24.8 + std::log(Threads.size()) / 2) * std::log(i));
}
contempt = (us == WHITE ? make_score(ct, ct / 2)
: -make_score(ct, ct / 2));
+ int searchAgainCounter = 0;
+
// Iterative deepening loop until requested to stop or the target depth is reached
while ( ++rootDepth < MAX_PLY
&& !Threads.stop
size_t pvFirst = 0;
pvLast = 0;
+ if (!Threads.increaseDepth)
+ searchAgainCounter++;
+
// MultiPV loop. We perform a full root search for each PV line
for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx)
{
if (rootDepth >= 4)
{
Value previousScore = rootMoves[pvIdx].previousScore;
- delta = Value(21 + abs(previousScore) / 128);
+ delta = Value(21 + abs(previousScore) / 256);
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 + (111 - ct / 2) * previousScore / (abs(previousScore) + 176);
+ int dct = ct + (102 - ct / 2) * previousScore / (abs(previousScore) + 157);
contempt = (us == WHITE ? make_score(dct, dct / 2)
: -make_score(dct, dct / 2));
int failedHighCnt = 0;
while (true)
{
- Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt);
+ Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
&& !Threads.stop
&& !mainThread->stopOnPonderhit)
{
- double fallingEval = (354 + 6 * (mainThread->previousScore - bestValue)
- + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 692.0;
+ double fallingEval = (332 + 6 * (mainThread->previousScore - bestValue)
+ + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 704.0;
fallingEval = clamp(fallingEval, 0.5, 1.5);
// If the bestMove is stable over several iterations, reduce time accordingly
- timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.97 : 0.98;
- double reduction = (1.36 + mainThread->previousTimeReduction) / (2.29 * timeReduction);
+ timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.94 : 0.91;
+ double reduction = (1.41 + mainThread->previousTimeReduction) / (2.27 * timeReduction);
// Use part of the gained time from a previous stable move for the current move
for (Thread* th : Threads)
else
Threads.stop = true;
}
+ else if ( Threads.increaseDepth
+ && Time.elapsed() > Time.optimum() * fallingEval * reduction * bestMoveInstability * 0.6)
+ Threads.increaseDepth = false;
+ else
+ Threads.increaseDepth = true;
}
mainThread->iterValue[iterIdx] = bestValue;
update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
}
}
- return ttValue;
+
+ if (pos.rule50_count() < 90)
+ return ttValue;
}
// Step 5. Tablebases probe
tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
- // Step 7. Razoring (~2 Elo)
+ // Step 7. Razoring (~1 Elo)
if ( !rootNode // The required rootNode PV handling is not available in qsearch
&& depth < 2
&& eval <= alpha - RazorMargin)
return qsearch<NT>(pos, ss, alpha, beta);
- improving = ss->staticEval >= (ss-2)->staticEval
- || (ss-2)->staticEval == VALUE_NONE;
+ improving = (ss-2)->staticEval == VALUE_NONE ? (ss->staticEval >= (ss-4)->staticEval
+ || (ss-4)->staticEval == VALUE_NONE) : ss->staticEval >= (ss-2)->staticEval;
- // Step 8. Futility pruning: child node (~30 Elo)
+ // Step 8. Futility pruning: child node (~50 Elo)
if ( !PvNode
- && depth < 7
+ && depth < 6
&& eval - futility_margin(depth, improving) >= beta
&& eval < VALUE_KNOWN_WIN) // Do not return unproven wins
return eval;
// Step 9. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 22661
+ && (ss-1)->statScore < 23397
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 33 * depth + 299 - improving * 30
+ && ss->staticEval >= beta - 32 * depth + 292 - 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 = (835 + 70 * depth) / 256 + std::min(int(eval - beta) / 185, 3);
+ Depth R = (854 + 68 * depth) / 258 + std::min(int(eval - beta) / 192, 3);
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
&& depth >= 5
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
- Value raisedBeta = std::min(beta + 191 - 46 * improving, VALUE_INFINITE);
+ Value raisedBeta = std::min(beta + 189 - 45 * improving, VALUE_INFINITE);
MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory);
int probCutCount = 0;
}
}
- // Step 11. Internal iterative deepening (~2 Elo)
+ // Step 11. Internal iterative deepening (~1 Elo)
if (depth >= 7 && !ttMove)
{
search<NT>(pos, ss, alpha, beta, depth - 7, cutNode);
// Calculate new depth for this move
newDepth = depth - 1;
- // Step 13. Pruning at shallow depth (~170 Elo)
+ // Step 13. Pruning at shallow depth (~200 Elo)
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_MATED_IN_MAX_PLY)
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
continue;
- // Futility pruning: parent node (~2 Elo)
+ // Futility pruning: parent node (~5 Elo)
if ( lmrDepth < 6
&& !inCheck
- && ss->staticEval + 250 + 211 * lmrDepth <= alpha)
+ && ss->staticEval + 255 + 182 * lmrDepth <= alpha
+ && thisThread->mainHistory[us][from_to(move)]
+ + (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)] < 30000)
continue;
- // Prune moves with negative SEE (~10 Elo)
- if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
+ // Prune moves with negative SEE (~20 Elo)
+ if (!pos.see_ge(move, Value(-(32 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
- else if (!pos.see_ge(move, Value(-199) * depth)) // (~20 Elo)
+ else if (!pos.see_ge(move, Value(-194) * depth)) // (~25 Elo)
continue;
}
- // Step 14. Extensions (~70 Elo)
+ // Step 14. Extensions (~75 Elo)
- // Singular extension search (~60 Elo). If all moves but one fail low on a
+ // Singular extension search (~70 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
// 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
extension = 1;
// Last captures extension
- else if ( PvNode
- && PieceValue[EG][pos.captured_piece()] > PawnValueEg
+ else if ( PieceValue[EG][pos.captured_piece()] > PawnValueEg
&& pos.non_pawn_material() <= 2 * RookValueMg)
extension = 1;
// Step 15. Make the move
pos.do_move(move, st, givesCheck);
- // Step 16. Reduced depth search (LMR). If the move fails high it will be
+ // Step 16. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be
// re-searched at full depth.
if ( depth >= 3
&& moveCount > 1 + 2 * rootNode
|| moveCountPruning
|| ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
|| cutNode
- || thisThread->ttHitAverage < 384 * ttHitAverageResolution * ttHitAverageWindow / 1024))
+ || thisThread->ttHitAverage < 375 * ttHitAverageResolution * ttHitAverageWindow / 1024))
{
Depth r = reduction(improving, depth, moveCount);
// Decrease reduction if the ttHit running average is large
- if (thisThread->ttHitAverage > 544 * ttHitAverageResolution * ttHitAverageWindow / 1024)
+ if (thisThread->ttHitAverage > 500 * ttHitAverageResolution * ttHitAverageWindow / 1024)
r--;
// Reduction if other threads are searching this position.
if (th.marked())
r++;
- // Decrease reduction if position is or has been on the PV
+ // Decrease reduction if position is or has been on the PV (~10 Elo)
if (ttPv)
r -= 2;
- // Decrease reduction if opponent's move count is high (~10 Elo)
- if ((ss-1)->moveCount > 15)
+ // Decrease reduction if opponent's move count is high (~5 Elo)
+ if ((ss-1)->moveCount > 14)
r--;
- // Decrease reduction if ttMove has been singularly extended
+ // Decrease reduction if ttMove has been singularly extended (~3 Elo)
if (singularLMR)
r -= 2;
if (!captureOrPromotion)
{
- // Increase reduction if ttMove is a capture (~0 Elo)
+ // Increase reduction if ttMove is a capture (~5 Elo)
if (ttCapture)
r++;
- // Increase reduction for cut nodes (~5 Elo)
+ // Increase reduction for cut nodes (~10 Elo)
if (cutNode)
r += 2;
// Decrease reduction for moves that escape a capture. Filter out
// castling moves, because they are coded as "king captures rook" and
- // hence break make_move(). (~5 Elo)
+ // hence break make_move(). (~2 Elo)
else if ( type_of(move) == NORMAL
&& !pos.see_ge(reverse_move(move)))
r -= 2;
+ (*contHist[0])[movedPiece][to_sq(move)]
+ (*contHist[1])[movedPiece][to_sq(move)]
+ (*contHist[3])[movedPiece][to_sq(move)]
- - 4729;
+ - 4926;
// Reset statScore to zero if negative and most stats shows >= 0
if ( ss->statScore < 0
ss->statScore = 0;
// Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= -99 && (ss-1)->statScore < -116)
+ if (ss->statScore >= -102 && (ss-1)->statScore < -114)
r--;
- else if ((ss-1)->statScore >= -117 && ss->statScore < -144)
+ else if ((ss-1)->statScore >= -116 && ss->statScore < -154)
r++;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 153;
+ futilityBase = bestValue + 154;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
projects / stockfish / blobdiff