/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2022 The Stockfish developers (see AUTHORS file)
+ Copyright (C) 2004-2023 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
// Futility margin
Value futility_margin(Depth d, bool improving) {
- return Value(165 * (d - improving));
+ return Value(158 * (d - improving));
}
// Reductions lookup table, initialized at startup
Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
int r = Reductions[d] * Reductions[mn];
- return (r + 1642 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 916);
+ return (r + 1460 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 937);
}
constexpr int futility_move_count(bool improving, Depth depth) {
// History and stats update bonus, based on depth
int stat_bonus(Depth d) {
- return std::min((12 * d + 282) * d - 349 , 1480);
+ return std::min(350 * d - 400, 1650);
}
// Add a small random component to draw evaluations to avoid 3-fold blindness
struct Skill {
Skill(int skill_level, int uci_elo) {
if (uci_elo)
- level = std::clamp(std::pow((uci_elo - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0);
+ {
+ double e = double(uci_elo - 1320) / (3190 - 1320);
+ level = std::clamp((((37.2473 * e - 40.8525) * e + 22.2943) * e - 0.311438), 0.0, 19.0);
+ }
else
level = double(skill_level);
}
bestPreviousScore = bestThread->rootMoves[0].score;
bestPreviousAverageScore = bestThread->rootMoves[0].averageScore;
- for (Thread* th : Threads)
- th->previousDepth = bestThread->completedDepth;
-
// Send again PV info if we have a new best thread
if (bestThread != this)
sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth) << sync_endl;
int iterIdx = 0;
std::memset(ss-7, 0, 10 * sizeof(Stack));
- for (int i = 7; i > 0; i--)
+ for (int i = 7; i > 0; --i)
+ {
(ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
+ (ss-i)->staticEval = VALUE_NONE;
+ }
for (int i = 0; i <= MAX_PLY + 2; ++i)
(ss+i)->ply = i;
multiPV = std::min(multiPV, rootMoves.size());
- complexityAverage.set(155, 1);
+ complexityAverage.set(153, 1);
optimism[us] = optimism[~us] = VALUE_ZERO;
if (rootDepth >= 4)
{
Value prev = rootMoves[pvIdx].averageScore;
- delta = Value(10) + int(prev) * prev / 15620;
+ delta = Value(10) + int(prev) * prev / 15400;
alpha = std::max(prev - delta,-VALUE_INFINITE);
beta = std::min(prev + delta, VALUE_INFINITE);
// Adjust optimism based on root move's previousScore
- int opt = 118 * prev / (std::abs(prev) + 169);
+ int opt = 116 * prev / (std::abs(prev) + 170);
optimism[ us] = Value(opt);
optimism[~us] = -optimism[us];
}
constexpr bool PvNode = nodeType != NonPV;
constexpr bool rootNode = nodeType == Root;
- const Depth maxNextDepth = rootNode ? depth : depth + 1;
// Check if we have an upcoming move which draws by repetition, or
// if the opponent had an alternative move earlier to this position.
if (!rootNode)
(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
- // position key in case of an excluded move.
+ // Step 4. Transposition table lookup.
excludedMove = ss->excludedMove;
- posKey = excludedMove == MOVE_NONE ? pos.key() : pos.key() ^ make_key(excludedMove);
+ posKey = pos.key();
tte = TT.probe(posKey, ss->ttHit);
ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
: ss->ttHit ? tte->move() : MOVE_NONE;
ttCapture = ttMove && pos.capture(ttMove);
+
+ // At this point, if excluded, skip straight to step 6, static eval. However,
+ // to save indentation, we list the condition in all code between here and there.
if (!excludedMove)
ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& ss->ttHit
+ && !excludedMove
&& tte->depth() > depth - (tte->bound() == BOUND_EXACT)
&& ttValue != VALUE_NONE // Possible in case of TT access race
&& (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
}
// Step 5. Tablebases probe
- if (!rootNode && TB::Cardinality)
+ if (!rootNode && !excludedMove && TB::Cardinality)
{
int piecesCount = pos.count<ALL_PIECES>();
complexity = 0;
goto moves_loop;
}
+ else if (excludedMove) {
+ // Providing the hint that this node's accumulator will be used often brings significant Elo gain (13 elo)
+ Eval::NNUE::hint_common_parent_position(pos);
+ eval = ss->staticEval;
+ complexity = abs(ss->staticEval - pos.psq_eg_stm());
+ }
else if (ss->ttHit)
{
// Never assume anything about values stored in TT
else
{
ss->staticEval = eval = evaluate(pos, &complexity);
-
// Save static evaluation into transposition table
- if (!excludedMove)
- tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
+ tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
-
thisThread->complexityAverage.update(complexity);
// Use static evaluation difference to improve quiet move ordering (~4 Elo)
if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
{
- int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1914, 1914);
+ int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1940, 1940);
thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
}
// margin and the improving flag are used in various pruning heuristics.
improvement = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval
: (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval
- : 168;
+ : 172;
improving = improvement > 0;
// Step 7. Razoring (~1 Elo).
// If eval is really low check with qsearch if it can exceed alpha, if it can't,
// return a fail low.
- if (eval < alpha - 369 - 254 * depth * depth)
+ if (eval < alpha - 394 - 255 * depth * depth)
{
value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
if (value < alpha)
// The depth condition is important for mate finding.
if ( !ss->ttPv
&& depth < 8
- && eval - futility_margin(depth, improving) - (ss-1)->statScore / 303 >= beta
+ && eval - futility_margin(depth, improving) - (ss-1)->statScore / 304 >= beta
&& eval >= beta
- && eval < 28031) // larger than VALUE_KNOWN_WIN, but smaller than TB wins
+ && eval < 28580) // larger than VALUE_KNOWN_WIN, but smaller than TB wins
return eval;
// Step 9. Null move search with verification search (~35 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 17139
+ && (ss-1)->statScore < 18200
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 20 * depth - improvement / 13 + 233 + complexity / 25
+ && ss->staticEval >= beta - 20 * depth - improvement / 14 + 235 + complexity / 24
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth, eval and complexity of position
- Depth R = std::min(int(eval - beta) / 168, 7) + depth / 3 + 4 - (complexity > 861);
+ Depth R = std::min(int(eval - beta) / 165, 6) + depth / 3 + 4 - (complexity > 800);
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
}
}
- probCutBeta = beta + 191 - 54 * improving;
+ probCutBeta = beta + 180 - 54 * improving;
// Step 10. ProbCut (~10 Elo)
// If we have a good enough capture and a reduced search returns a value
moves_loop: // When in check, search starts here
// Step 12. A small Probcut idea, when we are in check (~4 Elo)
- probCutBeta = beta + 417;
+ probCutBeta = beta + 402;
if ( ss->inCheck
&& !PvNode
&& depth >= 2
Value delta = beta - alpha;
+ Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
+
// Step 14. Pruning at shallow depth (~120 Elo). Depth conditions are important for mate finding.
if ( !rootNode
&& pos.non_pawn_material(us)
moveCountPruning = moveCount >= futility_move_count(improving, depth);
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, delta, thisThread->rootDelta), 0);
+ int lmrDepth = std::max(newDepth - r, 0);
if ( capture
|| givesCheck)
&& !PvNode
&& lmrDepth < 7
&& !ss->inCheck
- && ss->staticEval + 180 + 201 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
+ && ss->staticEval + 185 + 203 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
+ captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 6 < alpha)
continue;
// SEE based pruning (~11 Elo)
- if (!pos.see_ge(move, Value(-222) * depth))
+ if (!pos.see_ge(move, Value(-220) * depth))
continue;
}
else
// Continuation history based pruning (~2 Elo)
if ( lmrDepth < 5
- && history < -3875 * (depth - 1))
+ && history < -4180 * (depth - 1))
continue;
history += 2 * thisThread->mainHistory[us][from_to(move)];
+ lmrDepth += history / 7208;
+ lmrDepth = std::max(lmrDepth, -2);
+
// Futility pruning: parent node (~13 Elo)
if ( !ss->inCheck
&& lmrDepth < 13
- && ss->staticEval + 106 + 145 * lmrDepth + history / 52 <= alpha)
+ && ss->staticEval + 103 + 136 * lmrDepth <= alpha)
continue;
+ lmrDepth = std::max(lmrDepth, 0);
+
// Prune moves with negative SEE (~4 Elo)
- if (!pos.see_ge(move, Value(-24 * lmrDepth * lmrDepth - 15 * lmrDepth)))
+ if (!pos.see_ge(move, Value(-25 * lmrDepth * lmrDepth - 16 * lmrDepth)))
continue;
}
}
// 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 ( !rootNode
- && depth >= 4 - (thisThread->previousDepth > 24) + 2 * (PvNode && tte->is_pv())
+ && depth >= 4 - (thisThread->completedDepth > 22) + 2 * (PvNode && tte->is_pv())
&& move == ttMove
&& !excludedMove // Avoid recursive singular search
/* && ttValue != VALUE_NONE Already implicit in the next condition */
Depth singularDepth = (depth - 1) / 2;
ss->excludedMove = move;
+ // the search with excludedMove will update ss->staticEval
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
ss->excludedMove = MOVE_NONE;
// Check extensions (~1 Elo)
else if ( givesCheck
&& depth > 9
- && abs(ss->staticEval) > 82)
+ && abs(ss->staticEval) > 78)
extension = 1;
// Quiet ttMove extensions (~1 Elo)
else if ( PvNode
&& move == ttMove
&& move == ss->killers[0]
- && (*contHist[0])[movedPiece][to_sq(move)] >= 5177)
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 5600)
extension = 1;
}
// Step 16. Make the move
pos.do_move(move, st, givesCheck);
- Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
-
// Decrease reduction if position is or has been on the PV
// and node is not likely to fail low. (~3 Elo)
if ( ss->ttPv
if ((ss+1)->cutoffCnt > 3)
r++;
+ // Decrease reduction if move is a killer and we have a good history
+ if (move == ss->killers[0]
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 3600)
+ r--;
+
ss->statScore = 2 * thisThread->mainHistory[us][from_to(move)]
+ (*contHist[0])[movedPiece][to_sq(move)]
+ (*contHist[1])[movedPiece][to_sq(move)]
+ (*contHist[3])[movedPiece][to_sq(move)]
- - 4433;
+ - 4467;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r -= ss->statScore / (13000 + 4152 * (depth > 7 && depth < 19));
+ r -= ss->statScore / (12800 + 4410 * (depth > 7 && depth < 19));
// Step 17. Late moves reduction / extension (LMR, ~117 Elo)
// We use various heuristics for the sons of a node after the first son has
{
// Adjust full depth search based on LMR results - if result
// was good enough search deeper, if it was bad enough search shallower
- const bool doDeeperSearch = value > (alpha + 64 + 11 * (newDepth - d));
+ const bool doDeeperSearch = value > (alpha + 66 + 11 * (newDepth - d));
const bool doEvenDeeperSearch = value > alpha + 582 && ss->doubleExtensions <= 5;
const bool doShallowerSearch = value < bestValue + newDepth;
int bonus = value > alpha ? stat_bonus(newDepth)
: -stat_bonus(newDepth);
- if (capture)
- bonus /= 6;
-
update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
}
}
// Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1.
else if (!PvNode || moveCount > 1)
{
+ // Increase reduction for cut nodes and not ttMove (~1 Elo)
+ if (!ttMove && cutNode)
+ r += 2;
+
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 4), !cutNode);
}
(ss+1)->pv = pv;
(ss+1)->pv[0] = MOVE_NONE;
- value = -search<PV>(pos, ss+1, -beta, -alpha,
- std::min(maxNextDepth, newDepth), false);
+ value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
}
// Step 19. Undo move
quietsSearched, quietCount, capturesSearched, captureCount, depth);
// Bonus for prior countermove that caused the fail low
- else if ( (depth >= 5 || PvNode)
- && !priorCapture)
+ else if (!priorCapture)
{
- //Assign extra bonus if current node is PvNode or cutNode
- //or fail low was really bad
- bool extraBonus = PvNode
- || cutNode
- || bestValue < alpha - 62 * depth;
-
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + extraBonus));
+ // Extra bonuses for PV/Cut nodes or bad fail lows
+ int bonus = (depth > 4) + (PvNode || cutNode) + (bestValue < alpha - 88 * depth);
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * bonus);
}
if (PvNode)
bool pvHit, givesCheck, capture;
int moveCount;
+ // Step 1. Initialize node
if (PvNode)
{
(ss+1)->pv = pv;
ss->inCheck = pos.checkers();
moveCount = 0;
- // Check for an immediate draw or maximum ply reached
+ // Step 2. Check for an immediate draw or maximum ply reached
if ( pos.is_draw(ss->ply)
|| ss->ply >= MAX_PLY)
return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos) : VALUE_DRAW;
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
: DEPTH_QS_NO_CHECKS;
- // Transposition table lookup
+ // Step 3. Transposition table lookup
posKey = pos.key();
tte = TT.probe(posKey, ss->ttHit);
ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
ttMove = ss->ttHit ? tte->move() : MOVE_NONE;
pvHit = ss->ttHit && tte->is_pv();
+ // At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& ss->ttHit
&& tte->depth() >= ttDepth
&& (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
return ttValue;
- // Evaluate the position statically
+ // Step 4. Static evaluation of the position
if (ss->inCheck)
{
ss->staticEval = VALUE_NONE;
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 153;
+ futilityBase = bestValue + 158;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
int quietCheckEvasions = 0;
- // Loop through the moves until no moves remain or a beta cutoff occurs
+ // Step 5. Loop through all pseudo-legal moves until no moves remain
+ // or a beta cutoff occurs.
while ((move = mp.next_move()) != MOVE_NONE)
{
assert(is_ok(move));
moveCount++;
+ // Step 6. Pruning.
+ if (bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
+ {
// Futility pruning and moveCount pruning (~10 Elo)
- if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && !givesCheck
+ if ( !givesCheck
&& to_sq(move) != prevSq
&& futilityBase > -VALUE_KNOWN_WIN
&& type_of(move) != PROMOTION)
}
}
- // Do not search moves with negative SEE values (~5 Elo)
- if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && !pos.see_ge(move))
+ // We prune after 2nd quiet check evasion where being 'in check' is implicitly checked through the counter
+ // and being a 'quiet' apart from being a tt move is assumed after an increment because captures are pushed ahead.
+ if (quietCheckEvasions > 1)
+ break;
+
+ // Continuation history based pruning (~3 Elo)
+ if ( !capture
+ && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0
+ && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0)
+ continue;
+
+ // Do not search moves with bad enough SEE values (~5 Elo)
+ if (!pos.see_ge(move, Value(-108)))
continue;
+ }
+
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));
+ // Update the current move
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
[capture]
[pos.moved_piece(move)]
[to_sq(move)];
- // Continuation history based pruning (~3 Elo)
- if ( !capture
- && bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0
- && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0)
- continue;
-
- // We prune after 2nd quiet check evasion where being 'in check' is implicitly checked through the counter
- // and being a 'quiet' apart from being a tt move is assumed after an increment because captures are pushed ahead.
- if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && quietCheckEvasions > 1)
- break;
-
quietCheckEvasions += !capture && ss->inCheck;
- // Make and search the move
+ // Step 7. Make and search the move
pos.do_move(move, st, givesCheck);
value = -qsearch<nodeType>(pos, ss+1, -beta, -alpha, depth - 1);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Check for a new best move
+ // Step 8. Check for a new best move
if (value > bestValue)
{
bestValue = value;
}
}
+ // Step 9. Check for mate
// All legal moves have been searched. A special case: if we're in check
// and no legal moves were found, it is checkmate.
if (ss->inCheck && bestValue == -VALUE_INFINITE)
if (!pos.capture(bestMove))
{
- int bonus2 = bestValue > beta + 137 ? bonus1 // larger bonus
+ int bonus2 = bestValue > beta + 146 ? bonus1 // larger bonus
: stat_bonus(depth); // smaller bonus
// Increase stats for the best move in case it was a quiet move
projects / stockfish / blobdiff