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);
probCutBeta = beta + 209 - 44 * improving;
- // Step 9. ProbCut (~10 Elo)
+ // 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
&& ttValue != VALUE_NONE
&& ttValue < probCutBeta))
{
- // if ttMove is a capture and value from transposition table is good enough produce probCut
- // cutoff without digging into actual probCut search
- if ( ss->ttHit
- && tte->depth() >= depth - 3
- && ttValue != VALUE_NONE
- && ttValue >= probCutBeta
- && ttMove
- && pos.capture_or_promotion(ttMove))
- return probCutBeta;
-
assert(probCutBeta < VALUE_INFINITE);
MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
value = bestValue;
singularQuietLMR = moveCountPruning = 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.
movedPiece = pos.moved_piece(move);
givesCheck = pos.gives_check(move);
- // Indicate PvNodes that will probably fail low if node was searched with non-PV search
- // at depth equal or greater to current depth and result of this search was far below alpha
- bool likelyFailLow = PvNode
- && ttMove
- && (tte->bound() & BOUND_UPPER)
- && ttValue < alpha + 200 + 100 * depth
- && tte->depth() >= depth;
-
// Calculate new depth for this move
newDepth = depth - 1;
}
else
{
- // Countermoves based pruning (~20 Elo)
- if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
+ // Continuation history based pruning (~20 Elo)
+ if ( lmrDepth < 4
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
continue;
{
extension = 1;
singularQuietLMR = !ttCapture;
+ if (!PvNode && value < singularBeta - 140)
+ extension = 2;
}
// Multi-cut pruning
}
}
- // Check extension (~2 Elo)
- else if ( givesCheck
- && (pos.is_discovered_check_on_king(~us, move) || pos.see_ge(move)))
- extension = 1;
-
// Add extension to new depth
newDepth += extension;
|| ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
|| cutNode
|| (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 3678)
- || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024))
+ || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024)
+ && (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3))
{
Depth r = reduction(improving, depth, moveCount);
- // Decrease reduction if the ttHit running average is large
+ // Decrease reduction if the ttHit running average is large (~0 Elo)
if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024)
r--;
- // Increase reduction if other threads are searching this position
- if (th.marked())
- r++;
-
// Decrease reduction if position is or has been on the PV
- // and node is not likely to fail low. (~10 Elo)
+ // and node is not likely to fail low. (~3 Elo)
if ( ss->ttPv
&& !likelyFailLow)
r -= 2;
&& thisThread->bestMoveChanges <= 2)
r++;
- // More reductions for late moves if position was not in previous PV
- if ( moveCountPruning
- && !formerPv)
- r++;
-
- // Decrease reduction if opponent's move count is high (~5 Elo)
+ // 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--;
- if (captureOrPromotion)
- {
- // Increase reduction for non-checking captures likely to be bad
- if ( !givesCheck
- && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha)
- r++;
- }
- else
+ if (!captureOrPromotion)
{
- // Increase reduction if ttMove is a capture (~5 Elo)
+ // Increase reduction if ttMove is a capture (~3 Elo)
if (ttCapture)
r++;
// Increase reduction at root if failing high
- r += rootNode ? thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512 : 0;
+ if (rootNode)
+ r += thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512;
- // Increase reduction for cut nodes (~10 Elo)
+ // Increase reduction for cut nodes (~3 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 reverse_move() (~2 Elo)
- else if ( type_of(move) == NORMAL
- && !pos.see_ge(reverse_move(move)))
- r -= 2 + ss->ttPv - (type_of(movedPiece) == PAWN);
-
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)]
- 4741;
- // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= -89 && (ss-1)->statScore < -116)
- r--;
-
- else if ((ss-1)->statScore >= -112 && ss->statScore < -100)
- r++;
-
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- // If we are not in check use statScore, but if we are in check we use
- // the sum of main history and first continuation history with an offset.
- if (ss->inCheck)
- r -= (thisThread->mainHistory[us][from_to(move)]
- + (*contHist[0])[movedPiece][to_sq(move)] - 3833) / 16384;
- else
+ if (!ss->inCheck)
r -= ss->statScore / 14790;
}
[pos.moved_piece(move)]
[to_sq(move)];
- // CounterMove based pruning
+ // Continuation history based pruning
if ( !captureOrPromotion
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
projects / stockfish / blobdiff