[R-pkg-devel] How to get arbitrary precise inputs from R for an Rcpp package?

[Dirk Eddelbuettel]

Hi Khue,

On 19 July 2024 at 06:29, Khue Tran wrote:
| I am currently trying to get precise inputs by taking strings instead of
| numbers then writing a function to decompose the string into a rational
| with the denominator in the form of 10^(-n) where n is the number of
| decimal places. I am not sure if this is the only way or if there is a
| better method out there that I do not know of, so if you can think of a
| general way to get precise inputs from users, it will be greatly
| appreciated!

That is one possible way. The constraint really is that the .Call() interface
we use for all [1] extensions to R only knowns SEXP types which map to a
small set of known types: double, int, string, bool, ...  The type used by
the Boost library you are using is not among them, so you have to add code to
map back and forth. Rcpp makes that easier; it is still far from automatic.

R has packages such as Rmpfr interfacing GNU MPFR based on GMP. Maybe that is
good enough?  Also note that Rcpp has a dedicated (low volume and friendly)
mailing list where questions such as this one may be better suited.

Cheers, Dirk

[1] A slight generalisation. There are others but they are less common / not
recommended.

-- 
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