benchmark.h

// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef NDARRAY_EXAMPLES_BENCHMARK_H
#define NDARRAY_EXAMPLES_BENCHMARK_H

#include <algorithm>
#include <chrono>
#include <cmath>

namespace nda {

// Benchmark a call.
template <typename F>
double benchmark(F op) {
  const int max_trials = 10;
  const double min_time_s = 1;
  double time_per_iteration_s = 0;
  long iterations = 1;
  for (int trials = 0; trials < max_trials; trials++) {
    auto t1 = std::chrono::high_resolution_clock::now();
    for (int j = 0; j < iterations; j++) {
      op();
    }
    auto t2 = std::chrono::high_resolution_clock::now();
    time_per_iteration_s =
        std::chrono::duration_cast<std::chrono::nanoseconds>(t2 - t1).count() / (iterations * 1e9);
    if (time_per_iteration_s * iterations > min_time_s) { break; }

    long next_iterations = static_cast<long>(std::ceil((min_time_s * 2) / time_per_iteration_s));
    iterations = std::min(std::max(next_iterations, iterations), iterations * 10);
  }
  return time_per_iteration_s;
}

} // namespace nda

#endif // NDARRAY_EXAMPLES_BENCHMARK_H