offsetbenchmark.cpp

#include <chrono>
#include <iostream>
#include <type_traits>


template <class F, class... Args>
std::chrono::duration<double>
benchmark(F&& f, Args&&... args)
{
  using clock = std::conditional<std::chrono::high_resolution_clock::is_steady,
                                 std::chrono::high_resolution_clock,
                                 std::chrono::steady_clock>::type;
  const auto t0 = clock::now();
  std::forward<F>(f)(std::forward<Args>(args)...);
  return std::chrono::duration<double>(clock::now() - t0);
}

struct LargeOffset
{
  char a[128];
  char c;
};

struct SmallOffset
{
  char c;
  char a[128];
};

template<typename T>
void benchmarkOffset(T* t, int s)
{
  for (int i = 0; i != s; ++i) {
    t[i].c = 's';
  }
}

int main() {
  constexpr auto LENGTH = 10000000;
  SmallOffset* soa = new SmallOffset[LENGTH];
  LargeOffset* loa = new LargeOffset[LENGTH];
  std::cout << "Struct with small offset takes: " << benchmark(benchmarkOffset<SmallOffset>, soa, LENGTH).count() << std::endl;
  std::cout << "Struct with large offset takes: "<< benchmark(benchmarkOffset<LargeOffset>, loa, LENGTH).count() << std::endl;
  delete[] soa;
  delete[] loa;
}