Using rcpptimer with Rcpp::sourceCpp

Using Rcpp::Timer together with Rcpp::sourceCpp is similar to using it in an R package (c.f. vignette("packages")). However, instead of linking to rcpptimer in the DESCRIPTION file, we declare this dependency in the C++ file. We can do this by adding //[[Rcpp::depends(rcpptimer)]]. In the following, find a simple example file called ‘fibonacci_omp.cpp’:

// fibonacci_omp.cpp

//[[Rcpp::depends(rcpptimer)]]
#include <rcpptimer.h>

long int fib(long int n)
{
  return ((n <= 1) ? n : fib(n - 1) + fib(n - 2));
}

//[[Rcpp::export]]
std::vector<long int> fibonacci_omp(std::vector<long int> n)
{
  Rcpp::Timer timer;
  // This scoped timer measures the total execution time of 'fibonacci'
  Rcpp::Timer::ScopedTimer scpdtmr(timer, "fib_body");
  std::vector<long int> results = n;
#pragma omp parallel for
  for (unsigned int i = 0; i < n.size(); ++i)
  {
    timer.tic("fib_" + std::to_string(n[i]));
    results[i] = fib(n[i]);
    timer.toc("fib_" + std::to_string(n[i]));
  }
  return (results);
}

Place that file in your working directory and run:

Rcpp::sourceCpp("fibonacci_omp.cpp")

This will compile the C++ code and load the function fibonacci_omp into your R environment. You can now call it with fibonacci_omp(n = rep(20:25, 10)) and observe the timings by executing print(times).

Jonathan Berrisch

2024-09-22