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);
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;
}
}
- // 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;
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)
if ( ss->ttPv
&& 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)
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--;
}
else
{
- // Increase reduction if ttMove is a capture (~5 Elo)
+ // Increase reduction if ttMove is a capture (~3 Elo)
if (ttCapture)
r++;
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)]