/*
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) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2004-2021 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
#include "uci.h"
#include "syzygy/tbprobe.h"
+namespace Stockfish {
+
namespace Search {
LimitsType Limits;
namespace {
// Different node types, used as a template parameter
- enum NodeType { NonPV, PV };
+ enum NodeType { NonPV, PV, Root };
constexpr uint64_t TtHitAverageWindow = 4096;
constexpr uint64_t TtHitAverageResolution = 1024;
- // Razor and futility margins
- constexpr int RazorMargin = 531;
+ // Futility margin
Value futility_margin(Depth d, bool improving) {
- return Value(217 * (d - improving));
+ return Value(214 * (d - improving));
}
// Reductions lookup table, initialized at startup
Depth reduction(bool i, Depth d, int mn) {
int r = Reductions[d] * Reductions[mn];
- return (r + 511) / 1024 + (!i && r > 1007);
+ return (r + 534) / 1024 + (!i && r > 904);
}
constexpr int futility_move_count(bool improving, Depth depth) {
- return (4 + depth * depth) / (2 - improving);
+ return (3 + depth * depth) / (2 - improving);
}
// History and stats update bonus, based on depth
int stat_bonus(Depth d) {
- return d > 15 ? -8 : 19 * d * d + 155 * d - 132;
+ return d > 14 ? 73 : 6 * d * d + 229 * d - 215;
}
- // Add a small random component to draw evaluations to avoid 3fold-blindness
+ // Add a small random component to draw evaluations to avoid 3-fold blindness
Value value_draw(Thread* thisThread) {
return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
}
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>
+ template <NodeType nodeType>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
- template <NodeType NT>
+ template <NodeType nodeType>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0);
Value value_to_tt(Value v, int ply);
uint64_t perft(Position& pos, Depth depth) {
StateInfo st;
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
+
uint64_t cnt, nodes = 0;
const bool leaf = (depth == 2);
void Search::init() {
for (int i = 1; i < MAX_MOVES; ++i)
- Reductions[i] = int((24.8 + std::log(Threads.size())) * std::log(i));
+ Reductions[i] = int(21.9 * std::log(i));
}
Time.init(Limits, us, rootPos.game_ply());
TT.new_search();
+ Eval::NNUE::verify();
+
if (rootMoves.empty())
{
rootMoves.emplace_back(MOVE_NONE);
Thread* bestThread = this;
- if (int(Options["MultiPV"]) == 1 &&
- !Limits.depth &&
- !(Skill(Options["Skill Level"]).enabled() || int(Options["UCI_LimitStrength"])) &&
- rootMoves[0].pv[0] != MOVE_NONE)
+ if ( int(Options["MultiPV"]) == 1
+ && !Limits.depth
+ && !(Skill(Options["Skill Level"]).enabled() || int(Options["UCI_LimitStrength"]))
+ && rootMoves[0].pv[0] != MOVE_NONE)
bestThread = Threads.get_best_thread();
bestPreviousScore = bestThread->rootMoves[0].score;
// 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.
+ // The latter is needed for statScore and killer initialization.
Stack stack[MAX_PLY+10], *ss = stack+7;
Move pv[MAX_PLY+1];
Value bestValue, alpha, beta, delta;
for (int i = 7; i > 0; i--)
(ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
+ for (int i = 0; i <= MAX_PLY + 2; ++i)
+ (ss+i)->ply = i;
+
ss->pv = pv;
bestValue = delta = alpha = -VALUE_INFINITE;
// for match (TC 60+0.6) results spanning a wide range of k values.
PRNG rng(now());
double floatLevel = Options["UCI_LimitStrength"] ?
- Utility::clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) :
+ std::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);
multiPV = std::min(multiPV, rootMoves.size());
ttHitAverage = TtHitAverageWindow * TtHitAverageResolution / 2;
- int ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns
-
- // In analysis mode, adjust contempt in accordance with user preference
- if (Limits.infinite || Options["UCI_AnalyseMode"])
- ct = Options["Analysis Contempt"] == "Off" ? 0
- : Options["Analysis Contempt"] == "Both" ? ct
- : Options["Analysis Contempt"] == "White" && us == BLACK ? -ct
- : Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct
- : ct;
-
- // Evaluation score is from the white point of view
- contempt = (us == WHITE ? make_score(ct, ct / 2)
- : -make_score(ct, ct / 2));
+ trend = SCORE_ZERO;
int searchAgainCounter = 0;
if (rootDepth >= 4)
{
Value prev = rootMoves[pvIdx].previousScore;
- delta = Value(21);
+ delta = Value(17);
alpha = std::max(prev - delta,-VALUE_INFINITE);
beta = std::min(prev + delta, VALUE_INFINITE);
- // Adjust contempt based on root move's previousScore (dynamic contempt)
- int dct = ct + (102 - ct / 2) * prev / (abs(prev) + 157);
+ // Adjust trend based on root move's previousScore (dynamic contempt)
+ int tr = 113 * prev / (abs(prev) + 147);
- contempt = (us == WHITE ? make_score(dct, dct / 2)
- : -make_score(dct, dct / 2));
+ trend = (us == WHITE ? make_score(tr, tr / 2)
+ : -make_score(tr, tr / 2));
}
// Start with a small aspiration window and, in the case of a fail
while (true)
{
Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
- bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
+ bestValue = Stockfish::search<Root>(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
// is done with a stable algorithm because all the values but the
++failedHighCnt;
}
else
- {
- ++rootMoves[pvIdx].bestMoveCount;
break;
- }
delta += delta / 4 + 5;
&& !Threads.stop
&& !mainThread->stopOnPonderhit)
{
- double fallingEval = (332 + 6 * (mainThread->bestPreviousScore - bestValue)
- + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 704.0;
- fallingEval = Utility::clamp(fallingEval, 0.5, 1.5);
+ double fallingEval = (318 + 6 * (mainThread->bestPreviousScore - bestValue)
+ + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 825.0;
+ fallingEval = std::clamp(fallingEval, 0.5, 1.5);
// If the bestMove is stable over several iterations, reduce time accordingly
- timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.94 : 0.91;
- double reduction = (1.41 + mainThread->previousTimeReduction) / (2.27 * timeReduction);
+ timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.92 : 0.95;
+ double reduction = (1.47 + mainThread->previousTimeReduction) / (2.32 * 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();
+ double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth)
+ * totBestMoveChanges / Threads.size();
+ double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability;
- double totalTime = rootMoves.size() == 1 ? 0 :
- Time.optimum() * fallingEval * reduction * bestMoveInstability;
+ // Cap used time in case of a single legal move for a better viewer experience in tournaments
+ // yielding correct scores and sufficiently fast moves.
+ if (rootMoves.size() == 1)
+ totalTime = std::min(500.0, totalTime);
- // Stop the search if we have exceeded the totalTime, at least 1ms search.
+ // Stop the search if we have exceeded the totalTime
if (Time.elapsed() > totalTime)
{
// If we are allowed to ponder do not stop the search now but
}
else if ( Threads.increaseDepth
&& !mainThread->ponder
- && Time.elapsed() > totalTime * 0.6)
+ && Time.elapsed() > totalTime * 0.58)
Threads.increaseDepth = false;
else
Threads.increaseDepth = true;
// search<>() is the main search function for both PV and non-PV nodes
- template <NodeType NT>
+ template <NodeType nodeType>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
- constexpr bool PvNode = NT == PV;
- const bool rootNode = PvNode && ss->ply == 0;
+ 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 ( pos.rule50_count() >= 3
+ if ( !rootNode
+ && pos.rule50_count() >= 3
&& alpha < VALUE_DRAW
- && !rootNode
&& pos.has_game_cycle(ss->ply))
{
alpha = value_draw(pos.this_thread());
// Dive into quiescence search when the depth reaches zero
if (depth <= 0)
- return qsearch<NT>(pos, ss, alpha, beta);
+ return qsearch<PvNode ? PV : NonPV>(pos, ss, alpha, beta);
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64];
StateInfo st;
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
+
TTEntry* tte;
Key posKey;
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
- Value bestValue, value, ttValue, eval, maxValue;
- bool ttHit, ttPv, formerPv, givesCheck, improving, didLMR, priorCapture;
+ Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
+ bool givesCheck, improving, didLMR, priorCapture;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning,
ttCapture, singularQuietLMR;
Piece movedPiece;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
- ss->inCheck = pos.checkers();
- priorCapture = pos.captured_piece();
- Color us = pos.side_to_move();
- moveCount = captureCount = quietCount = ss->moveCount = 0;
- bestValue = -VALUE_INFINITE;
- maxValue = VALUE_INFINITE;
+ ss->inCheck = pos.checkers();
+ priorCapture = pos.captured_piece();
+ Color us = pos.side_to_move();
+ moveCount = captureCount = quietCount = ss->moveCount = 0;
+ bestValue = -VALUE_INFINITE;
+ maxValue = VALUE_INFINITE;
// Check for the available remaining time
if (thisThread == Threads.main())
|| pos.is_draw(ss->ply)
|| ss->ply >= MAX_PLY)
return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos)
- : value_draw(pos.this_thread());
+ : value_draw(pos.this_thread());
// Step 3. Mate distance pruning. Even if we mate at the next move our score
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
assert(0 <= ss->ply && ss->ply < MAX_PLY);
- (ss+1)->ply = ss->ply + 1;
+ (ss+1)->ttPv = false;
(ss+1)->excludedMove = bestMove = MOVE_NONE;
- (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
- Square prevSq = to_sq((ss-1)->currentMove);
+ (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+ ss->doubleExtensions = (ss-1)->doubleExtensions;
+ Square prevSq = to_sq((ss-1)->currentMove);
// Initialize statScore to zero for the grandchildren of the current position.
// So statScore is shared between all grandchildren and only the first grandchild
// 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
+ 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.
excludedMove = ss->excludedMove;
- posKey = pos.key() ^ Key(excludedMove << 16); // Isn't a very good hash
- tte = TT.probe(posKey, ttHit);
- ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
+ posKey = excludedMove == MOVE_NONE ? pos.key() : pos.key() ^ make_key(excludedMove);
+ 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]
- : ttHit ? tte->move() : MOVE_NONE;
- ttPv = PvNode || (ttHit && tte->is_pv());
- formerPv = ttPv && !PvNode;
-
- if (ttPv && depth > 12 && ss->ply - 1 < MAX_LPH && !pos.captured_piece() && is_ok((ss-1)->currentMove))
+ : ss->ttHit ? tte->move() : MOVE_NONE;
+ if (!excludedMove)
+ ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
+
+ // Update low ply history for previous move if we are near root and position is or has been in PV
+ if ( ss->ttPv
+ && depth > 12
+ && ss->ply - 1 < MAX_LPH
+ && !priorCapture
+ && is_ok((ss-1)->currentMove))
thisThread->lowPlyHistory[ss->ply - 1][from_to((ss-1)->currentMove)] << stat_bonus(depth - 5);
// thisThread->ttHitAverage can be used to approximate the running average of ttHit
thisThread->ttHitAverage = (TtHitAverageWindow - 1) * thisThread->ttHitAverage / TtHitAverageWindow
- + TtHitAverageResolution * ttHit;
+ + TtHitAverageResolution * ss->ttHit;
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
- && ttHit
+ && ss->ttHit
&& tte->depth() >= depth
&& ttValue != VALUE_NONE // Possible in case of TT access race
&& (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
{
if (ttValue >= beta)
{
+ // Bonus for a quiet ttMove that fails high
if (!pos.capture_or_promotion(ttMove))
update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth);
}
}
+ // Partial workaround for the graph history interaction problem
+ // For high rule50 counts don't produce transposition table cutoffs.
if (pos.rule50_count() < 90)
return ttValue;
}
if ( b == BOUND_EXACT
|| (b == BOUND_LOWER ? value >= beta : value <= alpha))
{
- tte->save(posKey, value_to_tt(value, ss->ply), ttPv, b,
+ tte->save(posKey, value_to_tt(value, ss->ply), ss->ttPv, b,
std::min(MAX_PLY - 1, depth + 6),
MOVE_NONE, VALUE_NONE);
// Step 6. Static evaluation of the position
if (ss->inCheck)
{
+ // Skip early pruning when in check
ss->staticEval = eval = VALUE_NONE;
improving = false;
- goto moves_loop; // Skip early pruning when in check
+ goto moves_loop;
}
- else if (ttHit)
+ else if (ss->ttHit)
{
// Never assume anything about values stored in TT
ss->staticEval = eval = tte->eval();
if (eval == VALUE_NONE)
ss->staticEval = eval = evaluate(pos);
+ // Randomize draw evaluation
if (eval == VALUE_DRAW)
eval = value_draw(thisThread);
}
else
{
+ // In case of null move search use previous static eval with a different sign
+ // and addition of two tempos
if ((ss-1)->currentMove != MOVE_NULL)
- {
- int bonus = -(ss-1)->statScore / 512;
-
- ss->staticEval = eval = evaluate(pos) + bonus;
- }
+ ss->staticEval = eval = evaluate(pos);
else
- ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo;
+ ss->staticEval = eval = -(ss-1)->staticEval;
- tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
+ // Save static evaluation into transposition table
+ if(!excludedMove)
+ tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
- // Step 7. Razoring (~1 Elo)
- if ( !rootNode // The required rootNode PV handling is not available in qsearch
- && depth == 1
- && eval <= alpha - RazorMargin)
- return qsearch<NT>(pos, ss, alpha, beta);
+ // Use static evaluation difference to improve quiet move ordering
+ if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
+ {
+ int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval), -1000, 1000);
+ thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
+ }
- improving = (ss-2)->staticEval == VALUE_NONE ? (ss->staticEval > (ss-4)->staticEval
- || (ss-4)->staticEval == VALUE_NONE) : ss->staticEval > (ss-2)->staticEval;
+ // Set up improving flag that is used in various pruning heuristics
+ // We define position as improving if static evaluation of position is better
+ // Than the previous static evaluation at our turn
+ // In case of us being in check at our previous move we look at move prior to it
+ 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 (~50 Elo)
+ // Step 7. Futility pruning: child node (~50 Elo)
if ( !PvNode
- && 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)
+ // Step 8. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 23397
+ && (ss-1)->statScore < 23767
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 32 * depth - 30 * improving + 120 * ttPv + 292
+ && ss->staticEval >= beta - 20 * depth - 22 * improving + 168 * ss->ttPv + 159
&& !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 = (854 + 68 * depth) / 258 + std::min(int(eval - beta) / 192, 3);
+ Depth R = (1090 + 81 * depth) / 256 + std::min(int(eval - beta) / 205, 3);
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
if (nullValue >= VALUE_TB_WIN_IN_MAX_PLY)
nullValue = beta;
- if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13))
+ if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 14))
return nullValue;
assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
}
}
- // Step 10. ProbCut (~10 Elo)
+ probCutBeta = beta + 209 - 44 * improving;
+
+ // Step 9. ProbCut (~4 Elo)
// If we have a good enough capture and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
- && depth >= 5
- && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY)
+ && depth > 4
+ && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY
+ // if value from transposition table is lower than probCutBeta, don't attempt probCut
+ // there and in further interactions with transposition table cutoff depth is set to depth - 3
+ // because probCut search has depth set to depth - 4 but we also do a move before it
+ // so effective depth is equal to depth - 3
+ && !( ss->ttHit
+ && tte->depth() >= depth - 3
+ && ttValue != VALUE_NONE
+ && ttValue < probCutBeta))
{
- Value raisedBeta = beta + 189 - 45 * improving;
- assert(raisedBeta < VALUE_INFINITE);
- MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &captureHistory);
+ assert(probCutBeta < VALUE_INFINITE);
+
+ MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
int probCutCount = 0;
+ bool ttPv = ss->ttPv;
+ ss->ttPv = false;
while ( (move = mp.next_move()) != MOVE_NONE
- && probCutCount < 2 + 2 * cutNode
- && !( move == ttMove
- && tte->depth() >= depth - 4
- && ttValue < raisedBeta))
+ && probCutCount < 2 + 2 * cutNode)
if (move != excludedMove && pos.legal(move))
{
assert(pos.capture_or_promotion(move));
pos.do_move(move, st);
// Perform a preliminary qsearch to verify that the move holds
- value = -qsearch<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1);
+ value = -qsearch<NonPV>(pos, ss+1, -probCutBeta, -probCutBeta+1);
// If the qsearch held, perform the regular search
- if (value >= raisedBeta)
- value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4, !cutNode);
+ if (value >= probCutBeta)
+ value = -search<NonPV>(pos, ss+1, -probCutBeta, -probCutBeta+1, depth - 4, !cutNode);
pos.undo_move(move);
- if (value >= raisedBeta)
+ if (value >= probCutBeta)
+ {
+ // if transposition table doesn't have equal or more deep info write probCut data into it
+ if ( !(ss->ttHit
+ && tte->depth() >= depth - 3
+ && ttValue != VALUE_NONE))
+ tte->save(posKey, value_to_tt(value, ss->ply), ttPv,
+ BOUND_LOWER,
+ depth - 3, move, ss->staticEval);
return value;
+ }
}
+ ss->ttPv = ttPv;
}
- // Step 11. Internal iterative deepening (~1 Elo)
- if (depth >= 7 && !ttMove)
- {
- search<NT>(pos, ss, alpha, beta, depth - 7, cutNode);
+ // Step 10. If the position is not in TT, decrease depth by 2
+ if ( PvNode
+ && depth >= 6
+ && !ttMove)
+ depth -= 2;
- tte = TT.probe(posKey, ttHit);
- ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
- ttMove = ttHit ? tte->move() : MOVE_NONE;
- }
+moves_loop: // When in check, search starts here
+
+ ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+
+ // Step 11. A small Probcut idea, when we are in check
+ probCutBeta = beta + 409;
+ if ( ss->inCheck
+ && !PvNode
+ && depth >= 4
+ && ttCapture
+ && (tte->bound() & BOUND_LOWER)
+ && tte->depth() >= depth - 3
+ && ttValue >= probCutBeta
+ && abs(ttValue) <= VALUE_KNOWN_WIN
+ && abs(beta) <= VALUE_KNOWN_WIN
+ )
+ return probCutBeta;
-moves_loop: // When in check, search starts from here
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
nullptr , (ss-4)->continuationHistory,
value = bestValue;
singularQuietLMR = moveCountPruning = false;
- ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+ bool doubleExtension = false;
- // Mark this node as being searched
- ThreadHolding th(thisThread, posKey, ss->ply);
+ // Indicate PvNodes that will probably fail low if the node was searched
+ // at a depth equal or greater than the current depth, and the result of this search was a fail low.
+ bool likelyFailLow = PvNode
+ && ttMove
+ && (tte->bound() & BOUND_UPPER)
+ && tte->depth() >= depth;
// Step 12. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
thisThread->rootMoves.begin() + thisThread->pvLast, move))
continue;
+ // Check for legality
+ if (!rootNode && !pos.legal(move))
+ continue;
+
ss->moveCount = ++moveCount;
if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
// Reduced depth of the next LMR search
int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
- if ( !captureOrPromotion
- && !givesCheck)
+ if ( captureOrPromotion
+ || givesCheck)
{
- // Countermoves based pruning (~20 Elo)
- 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 (~5 Elo)
- if ( lmrDepth < 6
- && !ss->inCheck
- && ss->staticEval + 235 + 172 * lmrDepth <= alpha
- && (*contHist[0])[movedPiece][to_sq(move)]
- + (*contHist[1])[movedPiece][to_sq(move)]
- + (*contHist[3])[movedPiece][to_sq(move)] < 27400)
+ // Capture history based pruning when the move doesn't give check
+ if ( !givesCheck
+ && lmrDepth < 1
+ && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
continue;
- // Prune moves with negative SEE (~20 Elo)
- if (!pos.see_ge(move, Value(-(32 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
+ // SEE based pruning
+ if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo)
continue;
}
else
{
- // Capture history based pruning when the move doesn't give check
- if ( !givesCheck
- && lmrDepth < 1
- && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
+ // Continuation history based pruning (~20 Elo)
+ if ( lmrDepth < 5
+ && (*contHist[0])[movedPiece][to_sq(move)] < (depth == 1 ? 0 : -stat_bonus(depth-1))
+ && (*contHist[1])[movedPiece][to_sq(move)] < (depth == 1 ? 0 : -stat_bonus(depth-1)))
continue;
- // Futility pruning for captures
- if ( !givesCheck
- && lmrDepth < 6
- && !(PvNode && abs(bestValue) < 2)
- && !ss->inCheck
- && ss->staticEval + 270 + 384 * lmrDepth + PieceValue[MG][type_of(pos.piece_on(to_sq(move)))] <= alpha)
+ // Futility pruning: parent node (~5 Elo)
+ if ( !ss->inCheck
+ && ss->staticEval + 174 + 157 * lmrDepth <= alpha
+ && (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)]
+ + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 28255)
continue;
- // See based pruning
- if (!pos.see_ge(move, Value(-194) * depth)) // (~25 Elo)
+ // Prune moves with negative SEE (~20 Elo)
+ if (!pos.see_ge(move, Value(-(30 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
}
// 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
- // result is lower than ttValue minus a margin then we will extend the ttMove.
- if ( depth >= 6
+ // result is lower than ttValue minus a margin, then we will extend the ttMove.
+ if ( !rootNode
+ && depth >= 7
&& move == ttMove
- && !rootNode
&& !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
- && pos.legal(move))
+ && tte->depth() >= depth - 3)
{
- Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2;
- Depth singularDepth = (depth - 1 + 3 * formerPv) / 2;
+ Value singularBeta = ttValue - 2 * depth;
+ Depth singularDepth = (depth - 1) / 2;
+
ss->excludedMove = move;
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
ss->excludedMove = MOVE_NONE;
{
extension = 1;
singularQuietLMR = !ttCapture;
+
+ // Avoid search explosion by limiting the number of double extensions to at most 3
+ if ( !PvNode
+ && value < singularBeta - 93
+ && ss->doubleExtensions < 3)
+ {
+ extension = 2;
+ doubleExtension = true;
+ }
}
// Multi-cut pruning
else if (singularBeta >= beta)
return singularBeta;
- // If the eval of ttMove is greater than beta we try also if there is an other move that
- // pushes it over beta, if so also produce a cutoff
+ // If the eval of ttMove is greater than beta we try also if there is another
+ // move that pushes it over beta, if so also produce a cutoff.
else if (ttValue >= beta)
{
ss->excludedMove = move;
return beta;
}
}
-
- // Check extension (~2 Elo)
- else if ( givesCheck
- && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move)))
- extension = 1;
-
- // Passed pawn extension
- else if ( move == ss->killers[0]
- && pos.advanced_pawn_push(move)
- && pos.pawn_passed(us, to_sq(move)))
- extension = 1;
-
- // Last captures extension
- else if ( PieceValue[EG][pos.captured_piece()] > PawnValueEg
- && pos.non_pawn_material() <= 2 * RookValueMg)
- extension = 1;
-
- // Castling extension
- if (type_of(move) == CASTLING)
+ else if ( givesCheck
+ && depth > 6
+ && abs(ss->staticEval) > Value(100))
extension = 1;
- // Late irreversible move extension
- if ( move == ttMove
- && pos.rule50_count() > 80
- && (captureOrPromotion || type_of(movedPiece) == PAWN))
- extension = 2;
-
// Add extension to new depth
newDepth += extension;
+ ss->doubleExtensions = (ss-1)->doubleExtensions + (extension == 2);
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));
- // Check for legality just before making the move
- if (!rootNode && !pos.legal(move))
- {
- ss->moveCount = --moveCount;
- continue;
- }
-
// Update the current move (this must be done after singular extension search)
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
// Step 15. Make the move
pos.do_move(move, st, givesCheck);
- // Step 16. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be
- // re-searched at full depth.
+ // Step 16. Late moves reduction / extension (LMR, ~200 Elo)
+ // We use various heuristics for the sons of a node after the first son has
+ // been searched. In general we would like to reduce them, but there are many
+ // cases where we extend a son if it has good chances to be "interesting".
if ( depth >= 3
&& moveCount > 1 + 2 * rootNode
- && (!rootNode || thisThread->best_move_count(move) == 0)
&& ( !captureOrPromotion
- || moveCountPruning
- || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
- || cutNode
- || thisThread->ttHitAverage < 375 * TtHitAverageResolution * TtHitAverageWindow / 1024))
+ || (cutNode && (ss-1)->moveCount > 1)
+ || !ss->ttPv)
+ && (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3))
{
Depth r = reduction(improving, depth, moveCount);
- // Decrease reduction if the ttHit running average is large
- if (thisThread->ttHitAverage > 500 * TtHitAverageResolution * TtHitAverageWindow / 1024)
+ if (PvNode)
r--;
- // Reduction if other threads are searching this position.
- if (th.marked())
- r++;
+ // Decrease reduction if the ttHit running average is large (~0 Elo)
+ if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024)
+ r--;
- // Decrease reduction if position is or has been on the PV (~10 Elo)
- if (ttPv)
+ // Decrease reduction if position is or has been on the PV
+ // and node is not likely to fail low. (~3 Elo)
+ if ( ss->ttPv
+ && !likelyFailLow)
r -= 2;
- if (moveCountPruning && !formerPv)
+ // Increase reduction at root and non-PV nodes when the best move does not change frequently
+ if ( (rootNode || !PvNode)
+ && thisThread->bestMoveChanges <= 2)
r++;
- // Decrease reduction if opponent's move count is high (~5 Elo)
- if ((ss-1)->moveCount > 14)
+ // Decrease reduction if opponent's move count is high (~1 Elo)
+ if ((ss-1)->moveCount > 13)
r--;
- // Decrease reduction if ttMove has been singularly extended (~3 Elo)
+ // Decrease reduction if ttMove has been singularly extended (~1 Elo)
if (singularQuietLMR)
- r -= 1 + formerPv;
+ r--;
- if (!captureOrPromotion)
- {
- // Increase reduction if ttMove is a capture (~5 Elo)
- if (ttCapture)
- r++;
-
- // 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(). (~2 Elo)
- else if ( type_of(move) == NORMAL
- && !pos.see_ge(reverse_move(move)))
- r -= 2 + ttPv;
-
- 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)]
- - 4926;
-
- // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= -102 && (ss-1)->statScore < -114)
- r--;
-
- else if ((ss-1)->statScore >= -116 && ss->statScore < -154)
- r++;
-
- // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r -= ss->statScore / 16434;
- }
- else
- {
- // Increase reduction for captures/promotions if late move and at low depth
- if (depth < 8 && moveCount > 2)
- r++;
-
- // Unless giving check, this capture is likely bad
- if ( !givesCheck
- && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 200 * depth <= alpha)
- r++;
- }
+ // Increase reduction for cut nodes (~3 Elo)
+ if (cutNode && move != ss->killers[0])
+ r += 2;
- Depth d = Utility::clamp(newDepth - r, 1, newDepth);
+ // Increase reduction if ttMove is a capture (~3 Elo)
+ if (ttCapture)
+ r++;
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
+ 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)]
+ - 4923;
+
+ // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
+ r -= ss->statScore / 14721;
+
+ // In general we want to cap the LMR depth search at newDepth. But if
+ // reductions are really negative and movecount is low, we allow this move
+ // to be searched deeper than the first move, unless ttMove was extended by 2.
+ Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5 && !doubleExtension));
- doFullDepthSearch = value > alpha && d != newDepth;
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
+ // If the son is reduced and fails high it will be re-searched at full depth
+ doFullDepthSearch = value > alpha && d < newDepth;
didLMR = true;
}
else
{
doFullDepthSearch = !PvNode || moveCount > 1;
-
didLMR = false;
}
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+ // If the move passed LMR update its stats
if (didLMR && !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);
}
}
(ss+1)->pv = pv;
(ss+1)->pv[0] = MOVE_NONE;
- value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
+ value = -search<PV>(pos, ss+1, -beta, -alpha,
+ std::min(maxNextDepth, newDepth), false);
}
// Step 18. Undo move
rm.pv.push_back(*m);
// 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.
+ // iteration. This information is used for time management and LMR
if (moveCount > 1)
++thisThread->bestMoveChanges;
}
else
{
assert(value >= beta); // Fail high
- ss->statScore = 0;
break;
}
}
}
+ // If the move is worse than some previously searched move, remember it to update its stats later
if (move != bestMove)
{
if (captureOrPromotion && captureCount < 32)
assert(moveCount || !ss->inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
if (!moveCount)
- bestValue = excludedMove ? alpha
- : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW;
+ bestValue = excludedMove ? alpha :
+ ss->inCheck ? mated_in(ss->ply)
+ : VALUE_DRAW;
+ // If there is a move which produces search value greater than alpha we update stats of searched moves
else if (bestMove)
update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq,
quietsSearched, quietCount, capturesSearched, captureCount, depth);
if (PvNode)
bestValue = std::min(bestValue, maxValue);
+ // If no good move is found and the previous position was ttPv, then the previous
+ // opponent move is probably good and the new position is added to the search tree.
+ if (bestValue <= alpha)
+ ss->ttPv = ss->ttPv || ((ss-1)->ttPv && depth > 3);
+ // Otherwise, a counter move has been found and if the position is the last leaf
+ // in the search tree, remove the position from the search tree.
+ else if (depth > 3)
+ ss->ttPv = ss->ttPv && (ss+1)->ttPv;
+
+ // Write gathered information in transposition table
if (!excludedMove && !(rootNode && thisThread->pvIdx))
- tte->save(posKey, value_to_tt(bestValue, ss->ply), ttPv,
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), ss->ttPv,
bestValue >= beta ? BOUND_LOWER :
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
depth, bestMove, ss->staticEval);
// 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>
+ template <NodeType nodeType>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
- constexpr bool PvNode = NT == PV;
+ static_assert(nodeType != Root);
+ constexpr bool PvNode = nodeType == PV;
assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
Move pv[MAX_PLY+1];
StateInfo st;
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
+
TTEntry* tte;
Key posKey;
Move ttMove, move, bestMove;
Depth ttDepth;
Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
- bool ttHit, pvHit, givesCheck, captureOrPromotion;
+ bool pvHit, givesCheck, captureOrPromotion;
int moveCount;
if (PvNode)
}
Thread* thisThread = pos.this_thread();
- (ss+1)->ply = ss->ply + 1;
bestMove = MOVE_NONE;
ss->inCheck = pos.checkers();
moveCount = 0;
: DEPTH_QS_NO_CHECKS;
// Transposition table lookup
posKey = pos.key();
- tte = TT.probe(posKey, ttHit);
- ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
- ttMove = ttHit ? tte->move() : MOVE_NONE;
- pvHit = ttHit && tte->is_pv();
+ 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();
if ( !PvNode
- && ttHit
+ && ss->ttHit
&& tte->depth() >= ttDepth
&& ttValue != VALUE_NONE // Only in case of TT access race
&& (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
}
else
{
- if (ttHit)
+ if (ss->ttHit)
{
// Never assume anything about values stored in TT
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
bestValue = ttValue;
}
else
+ // In case of null move search use previous static eval with a different sign
+ // and addition of two tempos
ss->staticEval = bestValue =
(ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
- : -(ss-1)->staticEval + 2 * Tempo;
+ : -(ss-1)->staticEval;
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
{
- if (!ttHit)
+ // Save gathered info in transposition table
+ if (!ss->ttHit)
tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER,
DEPTH_NONE, MOVE_NONE, ss->staticEval);
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 154;
+ futilityBase = bestValue + 155;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
- // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
- // be generated.
+ // queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
+ // will be generated.
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
&thisThread->captureHistory,
contHist,
{
assert(is_ok(move));
+ // Check for legality
+ if (!pos.legal(move))
+ continue;
+
givesCheck = pos.gives_check(move);
captureOrPromotion = pos.capture_or_promotion(move);
moveCount++;
- // Futility pruning
- if ( !ss->inCheck
+ // Futility pruning and moveCount pruning
+ if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !givesCheck
&& futilityBase > -VALUE_KNOWN_WIN
- && !pos.advanced_pawn_push(move))
+ && type_of(move) != PROMOTION)
{
- assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
+
+ if (moveCount > 2)
+ continue;
futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
}
}
- // Don't search moves with negative SEE values
- if ( !ss->inCheck && !pos.see_ge(move))
+ // Do not search moves with negative SEE values
+ if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
+ && !pos.see_ge(move))
continue;
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));
- // Check for legality just before making the move
- if (!pos.legal(move))
- {
- moveCount--;
- continue;
- }
-
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
[captureOrPromotion]
[pos.moved_piece(move)]
[to_sq(move)];
+ // Continuation history based pruning
+ if ( !captureOrPromotion
+ && bestValue > VALUE_TB_LOSS_IN_MAX_PLY
+ && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
+ && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold)
+ continue;
+
// Make and search the move
pos.do_move(move, st, givesCheck);
- value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - 1);
+ value = -qsearch<nodeType>(pos, ss+1, -beta, -alpha, depth - 1);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
}
}
- // All legal moves have been searched. A special case: If we're in check
+ // 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)
+ {
+ assert(!MoveList<LEGAL>(pos).size());
+
return mated_in(ss->ply); // Plies to mate from the root
+ }
+ // Save gathered info in transposition table
tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
bestValue >= beta ? BOUND_LOWER :
PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
// value_to_tt() adjusts a mate or TB score from "plies to mate from the root" to
- // "plies to mate from the current position". standard scores are unchanged.
+ // "plies to mate from the current position". Standard scores are unchanged.
// The function is called before storing a value in the transposition table.
Value value_to_tt(Value v, int ply) {
}
- // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate or TB score
- // from the transposition table (which refers to the plies to mate/be mated
- // from current position) to "plies to mate/be mated (TB win/loss) from the root".
- // However, for mate scores, to avoid potentially false mate scores related to the 50 moves rule,
- // and the graph history interaction, return an optimal TB score instead.
+ // value_from_tt() is the inverse of value_to_tt(): it adjusts a mate or TB score
+ // from the transposition table (which refers to the plies to mate/be mated from
+ // current position) to "plies to mate/be mated (TB win/loss) from the root". However,
+ // for mate scores, to avoid potentially false mate scores related to the 50 moves rule
+ // and the graph history interaction, we return an optimal TB score instead.
Value value_from_tt(Value v, int ply, int r50c) {
PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
bonus1 = stat_bonus(depth + 1);
- bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
- : stat_bonus(depth); // smaller bonus
+ bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
+ : std::min(bonus1, stat_bonus(depth)); // smaller bonus
if (!pos.capture_or_promotion(bestMove))
{
+ // Increase stats for the best move in case it was a quiet move
update_quiet_stats(pos, ss, bestMove, bonus2, depth);
- // Decrease all the non-best quiet moves
+ // Decrease stats for all non-best quiet moves
for (int i = 0; i < quietCount; ++i)
{
thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2;
}
}
else
+ // Increase stats for the best move in case it was a capture move
captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1;
- // 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]))
+ // Extra penalty for a quiet early move that was not a TT move or
+ // main killer move in previous ply when it gets refuted.
+ if ( ((ss-1)->moveCount == 1 + (ss-1)->ttHit || ((ss-1)->currentMove == (ss-1)->killers[0]))
&& !pos.captured_piece())
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -bonus1);
- // Decrease all the non-best capture moves
+ // Decrease stats for all non-best capture moves
for (int i = 0; i < captureCount; ++i)
{
moved_piece = pos.moved_piece(capturesSearched[i]);
for (int i : {1, 2, 4, 6})
{
+ // Only update first 2 continuation histories if we are in check
if (ss->inCheck && i > 2)
break;
if (is_ok((ss-i)->currentMove))
void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth) {
+ // Update killers
if (ss->killers[0] != move)
{
ss->killers[1] = ss->killers[0];
thisThread->mainHistory[us][from_to(move)] << bonus;
update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
+ // Penalty for reversed move in case of moved piece not being a pawn
if (type_of(pos.moved_piece(move)) != PAWN)
thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus;
+ // Update countermove history
if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
}
- if (depth > 12 && ss->ply < MAX_LPH)
+ // Update low ply history
+ if (depth > 11 && ss->ply < MAX_LPH)
thisThread->lowPlyHistory[ss->ply][from_to(move)] << stat_bonus(depth - 7);
}
} // namespace
+
/// MainThread::check_time() is used to print debug info and, more importantly,
/// to detect when we are out of available time and thus stop the search.
{
bool updated = rootMoves[i].score != -VALUE_INFINITE;
- if (depth == 1 && !updated)
+ if (depth == 1 && !updated && i > 0)
continue;
- Depth d = updated ? depth : depth - 1;
+ Depth d = updated ? depth : std::max(1, depth - 1);
Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
+ if (v == -VALUE_INFINITE)
+ v = VALUE_ZERO;
+
bool tb = TB::RootInTB && abs(v) < VALUE_MATE_IN_MAX_PLY;
v = tb ? rootMoves[i].tbScore : v;
<< " multipv " << i + 1
<< " score " << UCI::value(v);
+ if (Options["UCI_ShowWDL"])
+ ss << UCI::wdl(v, pos.game_ply());
+
if (!tb && i == pvIdx)
ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
bool RootMove::extract_ponder_from_tt(Position& pos) {
StateInfo st;
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
+
bool ttHit;
assert(pv.size() == 1);
if (RootInTB)
{
// Sort moves according to TB rank
- std::sort(rootMoves.begin(), rootMoves.end(),
+ std::stable_sort(rootMoves.begin(), rootMoves.end(),
[](const RootMove &a, const RootMove &b) { return a.tbRank > b.tbRank; } );
// Probe during search only if DTZ is not available and we are winning
m.tbRank = 0;
}
}
+
+} // namespace Stockfish