[Rcpp-devel] Rcpp ISNAN slower than C ISNAN?

[William Dunlap]

Could the c++ slowdown be due to the fact that Rinternals.h defines ISNAN
differently for C and C++?  For C it uses the compiler's isnan macro, for
C++ it calls the function R_isnancpp.

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, Dec 13, 2016 at 5:04 AM, Christian Gunning <xian at unm.edu> wrote:

> > |    for (i = 0; i < numObjects; i++) {
> > |      for (j = 0; j < numCodes; j++) {
> > |        dist = 0;
> > |        for (k = 0; k < numVars; k++) {
> > |          if (!ISNAN(data[i * numVars + k])) {
> > |            tmp = data[i * numVars + k] - codes[j * numVars + k];
> >
> > Why not drop data and codes and use  sData1(i,k) - sData2(j,k)  ?
>
> Or better yet, just use the original code with NumericMatrix:
> sData1[i * numVars + k] does the right thing.
> I don't get any timing difference based on this change.
>
> Using Rcpp sugar
> (https://cran.r-project.org/package=Rcpp/vignettes/Rcpp-sugar.pdf),
> and moving the call outside the loop, appears to do the right thing.
>
> ## modified example
> ## see edits here:
> https://github.com/helmingstay/rcpp-timings/blob/
> master/diff/rcppdist.cpp#L24
> git clone https://github.com/helmingstay/rcpp-timings
> cd rcpp-timings/diff
> R --vanilla < glue.R
>
> best,
> Christian
>
> >
> > That still doesn't explain the slowdowns though.  Could you prepare a
> > _complete_ yet minimal example along with mock data?
> >
> > Dirk
> >
> > --
> > http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
> >
>
> --
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