[Rcpp-devel] Getting the exact arithmetic as in R when Rcpp is used?
Peng Yu
pengyu.ut at gmail.com
Mon Jul 8 13:51:56 CEST 2013
Hi,
The following shows the arithmetic in C++ is slightly different from
in R. Is there a way to get the exact arithmetic as in R?
~/dvcs_src/rexample/Rexample/cran/base/sum$ Rscript main_Rcpp.R
> library(inline)
> src='
+ Rcpp::NumericVector vec(vx);
+ double sum = 0;
+ for (int i=0; i<vec.size(); i++) {
+ sum += vec[i];
+ }
+ return Rcpp::wrap(sum);
+ '
> fun=cxxfunction(
+ signature(vx='numeric')
+ , src
+ , plugin='Rcpp'
+ )
Attaching package: ‘Rcpp’
The following object is masked from ‘package:inline’:
registerPlugin
> vx=rep(.1, 10)
> options(digits=22)
> fun(vx)
[1] 0.9999999999999998889777
> sum(vx)
[1] 1
>
--
Regards,
Peng
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