// Castling extension
if (type_of(move) == CASTLING)
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;