Hi,
This looks very similar to a problem Dirk faced in rewriting the DEOptim
package to use Rcpp (the RcppDE package is on the Rcpp svn repo).
Essentially the problem is that the Rcpp::Function is a C++ object that
calls back to R, with additional protection, which eventually calls C++.
You should be able to bypass this entirely and access directly the
pointer to the C++ function from the R variable. This way, you stay in
the C++ world. This would allow you to branch your code depending on
whether you loop over a pure R function or a C++ function.
I'll cook an example.
Romain
Le 03/08/11 08:22, Manuel Castejón Limas a écrit :
Dear all,
I'm rewriting the AMORE package using Rcpp --- in fact it's more like
I'm having a lot of fun while rewriting the AMORE package thanks to Rcpp.
Nevertheless, I'm facing this little problem that I hope it would be
pretty easy for you to solve.
Let's consider the C++ function Tanh_f0
double
Tanh_f0(double inducedLocalField)
{
return tanh(inducedLocalField);
}
After compilation using inline, Tanh_f0 is exposed to R using Module
and accessible through actMod$Tanh_f0
actMod$Tanh_f0(0.1)
# [1] 0.09966799
Now, I want to pass actMod$Tanh_f0 as a parameter of a function in
order to use the original C++ function Tanh_f0.
testCode <- ' Rcpp::Function fx (myfun);
double result = as<double>(fx(x));
return wrap( result );
'
usingTanhf0 <- cfunction(sig=signature(myfun="function", x="numeric"),
body=testCode,…)
And that indeed works, but when compared to using a simple tanh
function it shows quite a bad performance.
testCode <- ' double value = as<double>(x);
double result = tanh(value);
return wrap( result );
'
usingTanh <- cfunction(sig=signature(x="numeric"), body=testCode, … )
benchmark(usingTanhf0(myfun=actMod$Tanh_f0, x=0.1) , usingTanh(
x=0.1), columns=c("test", "replications", "elapsed", "relative"),
order="relative", replications=1000)
# test replications elapsed
relative
# 2 usingTanh(x = 0.1) 1000 0.004
1
# 1 usingTanhf0(myfun = actMod$Tanh_f0, x = 0.1) 1000 0.080
20
Looks like having to go the R way to get access to Tanh_f0 has a high
cost. In order to be faster, it would be great if I could have access
to the original Tanh_f0 which I guess is pointed to by
actMod$Tanh_f0, may be at the address 0x100153d30 ?
actMod$Tanh_f0
# internal C++ function <0x100153d30>
# signature : double Tanh_f0(double)
After having had a look at RppDE sources, I guess the solution would
be to pass the function as an external pointer; something like :
testCode <- '
typedef double (*funPtr)(double) ;
Rcpp::XPtr< funPtr > fx (myfun);
double result = (*fx)(0.1);
return wrap( result );
'
testCodefun <- cfunction(sig=signature(myfun="C++Function"),
body=testCode,…)
result <- testCodefun(myfun=actMod$Tanh_f0)
But this does NOT work and crashes R.
Any hints?
Thank you for your patience in reading such long message!
Manuel
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Romain Francois
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