title: How to check in C# if the given double number is normal, i.e. is neither zero, subnormal, infinite, nor NaN
body: <p>How to check in C# if the given double number is normal, i.e. is neither zero, subnormal, infinite, nor NaN.</p>
  
  <p>In C++ there was a method std::isnormal which was exactly checking this condition. 
  Is there an equivalent in C#?</p>