code for the post https://cppbenchmarks.wordpress.com/2020/11/10/float-division-vs-multiplication-speed/

multiplication_vs_division.cpp

// source code for the post https://cppbenchmarks.wordpress.com/2020/11/10/float-division-vs-multiplication-speed/

#include <array>
#include <chrono>
#include <numeric>
#include <iostream>

float doNotOptimizeAway = 0.0F;

template <int nElements> std::chrono::microseconds benchmarkMultiplicationF32() {
  srand(0);

  std::array<float, nElements> data;
  for (int i = 0; i < nElements; ++i) {
    data[i] = rand();
  }

  const auto start = std::chrono::steady_clock::now();

  for (float &f : data) {
    f *= 0.3333333333F;
  }

  const auto end = std::chrono::steady_clock::now();

  doNotOptimizeAway += std::accumulate(data.begin(), data.end(), 1, std::multiplies<float>());

  return std::chrono::duration_cast<std::chrono::microseconds>(end - start);
}

template <int nElements> std::chrono::microseconds benchmarkDivisionF32() {
  srand(0);

  std::array<float, nElements> data;
  for (int i = 0; i < nElements; ++i) {
    data[i] = rand();
  }

  const auto start = std::chrono::steady_clock::now();

  for (float &f : data) {
    f /= 3.0F;
  }

  const auto end = std::chrono::steady_clock::now();

  doNotOptimizeAway += std::accumulate(data.begin(), data.end(), 1, std::multiplies<float>());

  return std::chrono::duration_cast<std::chrono::microseconds>(end - start);
}

static auto getFastestRun = [](const int iterations, auto f) {
  std::chrono::microseconds minDuration{999999};

  for (int i = 0; i < iterations; ++i) {
    const std::chrono::microseconds duration = f();

    if (duration.count() < minDuration.count()) {
      minDuration = duration;
    }
  }

  std::cout << minDuration.count() << " µs\n";
};

auto main() -> int {
  constexpr int nElements = 200000;
  constexpr int nIterations = 5000;

  getFastestRun(nIterations, []() { return benchmarkMultiplicationF32<nElements>(); });
  getFastestRun(nIterations, []() { return benchmarkDivisionF32<nElements>(); });

  std::cout << "\n";

  return doNotOptimizeAway;
}