[Rcpp-devel] Sugar seems slower than Rcpp.

[Andrew Redd]

Cedric,
This was addressed  about 2 weeks ago on the list, please read the archives.
 Basic point, Rcpp/sugar will not be faster than basic functions in R. Do
something more complicated to see improvements.  I would suggest something
that involves lots of copies and edits, that will mess with R's memory
management but be much more efficient in compiled code.

-Andrew

On Tue, Jan 4, 2011 at 8:14 AM, Cedric Ginestet <c.ginestet05 at googlemail.com
> wrote:

>  Happy new year to everyone,
>
> I have made a very straightforward comparison of the performance of
> standard R, Rcpp function and sugar, and found that the latter produces the
> poorest performance. Let me know what you think and how I could improve such
> performance assessment.
>
> ###################################################
> Summing1 <- cxxfunction(signature(x="numeric"), '
>       NumericVector xV(x);
>       double out = sum(xV);
>       return wrap(out);
> ',plugin="Rcpp")
> Summing2 <- cxxfunction(signature(x="numeric"), '
>       NumericVector xV(x);
>       double out = 0.0;
>       for(int i=0; i<xV.size(); i++) out += xV[i];
>       return wrap(out);
> ',plugin="Rcpp")
> ###################################################
> # Results.
> n <- 1000000; x <- rnorm(n)
> Summing1(x); Summing2(x); sum(x)
> #######################
> gives:
> [1] -396.6129
> [1] -396.6129
> [1] -396.6129
>
> ###################################################
> # Time.
> system.time(Summing1(x));    # Sugar
> system.time(Summing2(x));    # Rcpp
> system.time(sum(x));               # R-base
> ###################
> > system.time(Summing1(x));
>    user  system elapsed
>   0.016   0.000   0.016
> > system.time(Summing2(x));
>    user  system elapsed
>   0.008   0.000   0.011
> > system.time(sum(x));
>    user  system elapsed
>   0.000   0.000   0.003
>
>
> Sugar appears to be the slowest! What about Rcpp basic loop? Why isn't as
> fast as the standard sum() in R-base?
> Cheers,
> Cedric
>
> --
>  Cedric Ginestet
> Centre for Neuroimaging Sciences (L3.04)
> NIHR Biomedical Research Centre
> Institute of Psychiatry, Box P089
> Kings College London
> De Crespigny Park
> London
> SE5 8AF
>
>
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>
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