This function is used to know if the library is compiled using integer 8 or 4 bytes long.
    function use_8bytes_int() bind(c, name='__use_8bytes_int')
        !! This function is used to know if the library is
        !! compiled using integer 8 or 4 bytes long.
        logical(kind=c_bool) :: use_8bytes_int
#ifdef USE_I8
        use_8bytes_int = .true.
#else
        use_8bytes_int = .false.
#endif
    end function use_8bytes_int