---------- Forwarded message ---------- From: Thell Fowler <tbfowl...@gmail.com> Date: Sun, Apr 22, 2012 at 11:18 AM Subject: Re: [Rcpp-devel] Example of rcpp usage with Rmpfr, mpfr, gmp. To: Dirk Eddelbuettel <e...@debian.org>
On Sun, Apr 22, 2012 at 10:49 AM, Dirk Eddelbuettel <e...@debian.org> wrote: > > Hi Thell, > > On 22 April 2012 at 10:17, Thell Fowler wrote: > > --- >8 --- > | Simple and straight forward... > | > | My two use cases are: > | > | 1) Pass input as 'numeric', convert to multiprecision 160-bit, do > | calculations using multiprecision lgamma values, and return an mpfr array > | object. > | 2) Pass input as mpfr objects (list or array), do calculations, and > return > | the modified values. > | > | Any examples or direction on how (if I can) to get to a Rcpp Rmpfr > bridge with > | speed would go a long way... > > Sounds fine. Not sure how to return (or pass down) the mpfr arrays. But > you may be able to > look at the existing CRAN packages wrapping mpfr for ideas. > > I'll try reading through the Rmpfr source to see how it does its' magic. Also, the Bessel package depends on Rmpfr so that might yield some ideas. As a really simple minded idea, you can > > 1) use Rcpp to pass values from R down to a C/C++ layer > > 2) "cast" or copy your values into mpfr et al types, do you computations > and get the result, cast/copy it back to C/C++ > > 3) use Rcpp to communicate back up > > which is pretty standard use of Rcpp to call external libraries or > packages. Many of the CRAN packages using Rcpp do something similar. > > I'll take a closer look at how this works. At first thought I wonder what the function sig would use for the type? Some sort of 'raw' type ? You just need to add the required -I and -L flags to src/Makevars and you > should be fine. [ Higher-end solutions use configure, or pkg-config, or > ... to find those values. Harcoded may work on standard Linux systems. ] > > That part _should_ be pretty straight forward. [ And if you want to look into doing more of an integration (a la > RcppArmadillo, > RcppGSL, RcppEigen, ...), then the Rcpp-extending vignette shows you how to > modify as<>() and wrap() to get automatic converters going. But you surely > don't need to do this for a first attempt to compute your stuff. I just > mention it as you say 'R mpfr bridge' -- this would be the Rcpp way of > doing > it. ] > > Cheers, Dirk > > The Rcpp-extending vignette is what I originally thought would be the answer. Good thing I asked first! ;) -- Sincerely, Thell -- Sincerely, Thell
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