[Rcpp-devel] Sugar seems slower than Rcpp.

[Cedric Ginestet]

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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