#include <Rcpp.h>
// [[Rcpp::depends(RcppParallel)]]
#include <RcppParallel.h>
#include <cmath>
#include <algorithm>

using namespace Rcpp;
using namespace RcppParallel;

// [[Rcpp::export]]
Rcpp::NumericVector SqrtCpp(Rcpp::NumericVector orig) {

  // allocate the matrix we will return
  NumericVector res(orig.begin(), orig.end());

  // transform it
  std::transform(orig.begin(), orig.end(), res.begin(), ::sqrt);

  // return the new matrix
  return res;
}


struct SquareRoot : public Worker
{
  const RVector<double> input;

  RVector<double> output;

  SquareRoot(const NumericVector input, NumericVector output)
    : input(input), output(output) {}

  void operator()(std::size_t begin, std::size_t end) {
    std::transform(input.begin() + begin,
                   input.begin() + end,
                   output.begin() + begin,
                   ::sqrt);
  }
};


// [[Rcpp::export]]
Rcpp::NumericVector SqrtCppPara(Rcpp::NumericVector x) {

  // allocate the output matrix
  NumericVector output(x.begin(), x.end());

  // SquareRoot functor (pass input and output matrixes)
  SquareRoot squareRoot(x, output);

  // call parallelFor to do the work
  parallelFor(0, x.length(), squareRoot);

  // return the output matrix
  return output;
}