offset.cpp

#include "benchmark.h"

#include <iostream>
#include <fstream>

constexpr auto LENGTH = 10000000;
constexpr auto ITERATIONS = 100;

template<int N>
struct LargeOffset {
  char a[N];
  char c;
};

template<int N>
struct SmallOffset {
  char c;
  char a[N];
};

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

template <int N>
std::pair<double, double> runBenchmark() {
  SmallOffset<N>* soa = new SmallOffset<N>[LENGTH];
  LargeOffset<N>* loa = new LargeOffset<N>[LENGTH];
  const double d1 = benchmark(benchmarkOffset<SmallOffset<N>>, soa, LENGTH).count();
  const double d2 = benchmark(benchmarkOffset<LargeOffset<N>>, loa, LENGTH).count();
  delete[] soa;
  delete[] loa;
  return {d1, d2};
}

template <int N>
void run_benchmarks() {
  double s1 = 0;
  double s2 = 0;

  for (int i = 0; i != ITERATIONS; ++i) {
    auto p = runBenchmark<N>();
    s1 += p.first;
    s2 += p.second;
  }

  s1 = s1 / ITERATIONS;
  s2 = s2 / ITERATIONS;
  std::cout << N << ":" << std::endl;
  std::cout << "Small offset: " << s1 << std::endl;
  std::cout << "Large offset: " << s2 << std::endl;

  {
    std::ofstream outfile;
    outfile.open("results.csv", std::ios_base::app);
    outfile << N << ',' << s1 << ',' << s2 << ',' << (s2-s1) << std::endl;
  }

  run_benchmarks<N-1>();
}

template<>
void run_benchmarks<0>() {
  // terminate loop
}

int main() { 

  {
    std::ofstream outfile;
    outfile.open("results.csv");
    outfile << "Byte Offset, Large, Small, Difference" << std::endl;
  }
  run_benchmarks<130>();
}