1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
/**
* @title Summing a Vector in Parallel with RcppParallel
* @author JJ Allaire
* @license GPL (>= 2)
*/
#include <Rcpp.h>
#include <RcppParallel.h>
// [[Rcpp::depends(RcppParallel)]]
using namespace RcppParallel;
using namespace Rcpp;
struct Sum : public Worker
{
// source vector
const RVector<double> input;
// accumulated value
double value;
// constructors
Sum(const NumericVector input) : input(input), value(0) {}
Sum(const Sum& sum, Split) : input(sum.input), value(0) {}
// accumulate just the element of the range I have been asked to
void operator()(std::size_t begin, std::size_t end) {
value += std::accumulate(input.begin() + begin, input.begin() + end, 0.0);
}
// join my value with that of another Sum
void join(const Sum& rhs) {
value += rhs.value;
}
};
// [[Rcpp::export]]
double parallelVectorSum(NumericVector x) {
// declare the SumBody instance
Sum sum(x);
// call parallel_reduce to start the work
parallelReduce(0, x.length(), sum);
// return the computed sum
return sum.value;
}
// [[Rcpp::export]]
double vectorSum(NumericVector x) {
return std::accumulate(x.begin(), x.end(), 0.0);
}
|
