[Rcpp-devel] New self-contained OpenMP example (Was: Stack imbalance warning when using Rcpp and OpenMP)

[Davor Cubranic]

On August 25, 2011 05:32:45 PM Dirk Eddelbuettel wrote:
> Long story short I just committed a new self-contained example to the Rcpp
> source which you can look at (and copy) via the URL
[...]
> The results bear this out. On my (standard i7, four cores hyperthreaded)
> box:
> 
> edd at max:~$ r ~/svn/rcpp/pkg/Rcpp/inst/examples/OpenMP/OpenMPandInline.r
> Loading required package: methods
>               test replications elapsed relative user.self sys.self
> 2     funOpenMP(z)          100   3.219 1.000000     25.26     0.07
> 3 funSerialRcpp(z)          100   9.030 2.805219      9.43     0.32
> 4  funSugarRcpp(z)          100   9.423 2.927307      9.06     0.35
> 1     funSerial(z)          100   9.601 2.982603      9.59     0.00
> edd at max:~$
> 
[...]
> Rcpp sugar has no real leg up on manual loops, but is the shortest
> implementation in two lines. Looping over an Rcpp vector is a little faster
> than looping over a C++ STL vector (which incurs a copy).

I know you wanted to keep all code looking the same, but with std::transform 
all serial code is very short:

serialStdAlgCode <- '
   std::vector<double> x = Rcpp::as<std::vector< double > >(xs);
   std::transform(x.begin(), x.end(), x.begin(), ::log);
   return Rcpp::wrap(x);
'
funSerialStdAlg <- cxxfunction(signature(xs="numeric"), body=serialStdAlgCode, 
plugin="Rcpp")

serialStdAlgRcppCode <- '
   Rcpp::NumericVector x = Rcpp::NumericVector(xs);
   std::transform(x.begin(), x.end(), x.begin(), ::log);
   return x;
'
funSerialStdAlgRcpp <- cxxfunction(signature(xs="numeric"), 
body=serialStdAlgRcppCode, plugin="Rcpp")

The results (without OpenMP because I'm currently on a single-core CPU):

                    test replications elapsed relative user.self sys.self
3 funSerialStdAlgRcpp(z)           20   4.236 1.000000     3.792    0.252
4       funSerialRcpp(z)           20   4.312 1.017941     3.792    0.272
5        funSugarRcpp(z)           20   4.537 1.071058     3.744    0.588
2     funSerialStdAlg(z)           20   5.514 1.301700     4.329    0.884
1           funSerial(z)           20   5.536 1.306893     4.480    0.808

Davor