const EC_Group_Data& EC_Group::data() const
   {
   if(m_data == nullptr)
      throw Invalid_State("EC_Group uninitialized");
   return *m_data;
   }
const EC_Group_Data& EC_Group::data() const
   {
   if(m_data == nullptr)
      throw Invalid_State("EC_Group uninitialized");
   return *m_data;
   }