lib/unseq.cpp

The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#include <execution>

int main (int argc, char** argv)
{
  // init number of argument from command line (default: 1000):
  int numElems = 1000;
  if (argc > 1) {
    numElems = std::atoi(argv[1]);
  }

  // init vector of different double values:
  std::vector<double> coll;
  coll.reserve(numElems);
  for (int i=0; i<numElems; ++i) {
    coll.push_back(i * 4.37);
  }

  // process square roots:
  // - allow SIMD processing but only one thread
  std::for_each(std::execution::unseq,     // since C++20
                coll.begin(), coll.end(),
                [](auto& val) {
                  val = std::sqrt(val);
                });

  for (double value : coll) {
    std::cout << value << '\n';
  }
}