Too many continuation lines for Fortran 2008

[jme52]

The README states that

To build this project from the source code in this repository you need a Fortran compiler supporting at least the Fortran 2008 standard.

However, in Fortran 2008

A statement shall not have more than 255 continuation lines.

(see paragraph 2 of section 3.3.2.6 of Fortran 2008). Unfortunately the statement that defines vdwrad in src/dftd3/data/vdwrad.f90 and the statements used to define the values of c6ab_view in src/dftd3/reference.f90 have more than 255 continuation lines.

Some compilers don't check this, but others do. The limit, combined with the maximum length of a line (132 characters) imposes a maximum of ~34k characters in a statement up to Fortran 2018 (see paragraph 2 of section 6.3.2.6 of Fortran 2018; the limit was the same since Fortran 2003, and smaller before that).

The latest version of the standard addressed this: in Fortran 2003 (see section 6.3.2),

A line shall contain at most ten thousand characters. [...]
A statement shall not have more than one million characters.

I think it's a bit too early and disproportionate to indicate in the README that "a Fortran compiler supporting Fortran 2023 is needed", so I was wondering if it would be reasonable to address this at the source code level:

• c6ab_view can be easily fixed by reducing the size of the chunks used to define the array, but I think that
• vdwrad needs a bit of code refactoring so that it is initialised from a module subroutine.