[R-pkg-devel] Modernizing legacy Fortran:, REAL(kind=8)

[Avraham Adler]

I’ve had no issues using the iso_c_binding schema. 

Avi

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> On Aug 30, 2023, at 2:43 AM, Thomas Petzoldt <thomas.petzoldt using tu-dresden.de> wrote:
> 
> Hi,
> 
> some package maintainers including me got a reminder from Prof. Brian Ripley to modernize REAL and INTEGER declarations using the KIND option:
> 
>> On 29.08.2023 at 19:31 Prof Brian Ripley wrote:
>> According to the Fortran standards, numerical values are just an enumeration, and what e.g. real(kind=4) means (or even if it is accepted) is implementation dependent.
>> We see such constructs in packages
> 
> [... line with packages deleted to avoid exposing the other packages and authors]
> 
>> Please change them to something portable (kind(1.0) or kind(1.0d0} are commonly used, as is c_double from iso_c_binding).
>> Before 2023-09-26 to safely retain your package on CRAN (some of you have earlier deadlines for other issues).
> 
> We use a lot of legacy code that though partly modernized due to similar requests, still uses a mix of DOUBLE PRECISION and a few REAL(KIND=8) and COMPLEX(KIND=8). As the code will still remain legacy style with respect to some other constructs, I wonder what to use to go a step forward, but remain as consistent as possible, which is of course a compromise. I see the following options:
> 
> a) change REAL(kind=8) back to DOUBLE PRECISION that is again old style. It seems to be portable and is still widely used.
> 
> b) just formally change the few occurrences to:REAL(kind=0.0d) as suggested. It is easy, but inconsistency remains.
> 
> c) or, define "dp" as recommended in modern style guides and use it instead of REAL(kind=8) and the future also for DOUBLE PRECISION this way:
> 
> integer,parameter::dp=kind(0.0d0)
> 
> and then
> 
> real(dp)::a,b,c
> 
> However, this would need changes at many places, the mix between old and new constructswill generally get worse.
> 
> Another question is, that with either of these, we may not be sure to use 8 byte double. Changing this could influence for precision and pointer arithmetics.
> 
> Any recommendations? Thanks a lot!
> 
> Thomas
> 
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