include/internal/benchmark/detail/catch_estimate_clock.hpp

/*
 *  Created by Joachim on 16/04/2019.
 *  Adapted from donated nonius code.
 *
 *  Distributed under the Boost Software License, Version 1.0. (See accompanying
 *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 */

 // Environment measurement

#ifndef TWOBLUECUBES_CATCH_DETAIL_ESTIMATE_CLOCK_HPP_INCLUDED
#define TWOBLUECUBES_CATCH_DETAIL_ESTIMATE_CLOCK_HPP_INCLUDED

#include "../catch_clock.hpp"
#include "../catch_environment.hpp"
#include "catch_stats.hpp"
#include "catch_measure.hpp"
#include "catch_run_for_at_least.hpp"
#include "../catch_clock.hpp"

#include <algorithm>
#include <iterator>
#include <tuple>
#include <vector>
#include <cmath>

namespace Catch {
    namespace Benchmark {
        namespace Detail {
            template <typename Clock>
            std::vector<double> resolution(int k) {
                std::vector<TimePoint<Clock>> times;
                times.reserve(k + 1);
                std::generate_n(std::back_inserter(times), k + 1, now<Clock>{});

                std::vector<double> deltas;
                deltas.reserve(k);
                std::transform(std::next(times.begin()), times.end(), times.begin(),
                    std::back_inserter(deltas),
                    [](TimePoint<Clock> a, TimePoint<Clock> b) { return static_cast<double>((a - b).count()); });

                return deltas;
            }

            const auto warmup_iterations = 10000;
            const auto warmup_time = std::chrono::milliseconds(100);
            const auto minimum_ticks = 1000;
            const auto warmup_seed = 10000;
            const auto clock_resolution_estimation_time = std::chrono::milliseconds(500);
            const auto clock_cost_estimation_time_limit = std::chrono::seconds(1);
            const auto clock_cost_estimation_tick_limit = 100000;
            const auto clock_cost_estimation_time = std::chrono::milliseconds(10);
            const auto clock_cost_estimation_iterations = 10000;

            template <typename Clock>
            int warmup() {
                return run_for_at_least<Clock>(std::chrono::duration_cast<ClockDuration<Clock>>(warmup_time), warmup_seed, &resolution<Clock>)
                    .iterations;
            }
            template <typename Clock>
            EnvironmentEstimate<FloatDuration<Clock>> estimate_clock_resolution(int iterations) {
                auto r = run_for_at_least<Clock>(std::chrono::duration_cast<ClockDuration<Clock>>(clock_resolution_estimation_time), iterations, &resolution<Clock>)
                    .result;
                return {
                    FloatDuration<Clock>(mean(r.begin(), r.end())),
                    classify_outliers(r.begin(), r.end()),
                };
            }
            template <typename Clock>
            EnvironmentEstimate<FloatDuration<Clock>> estimate_clock_cost(FloatDuration<Clock> resolution) {
                auto time_limit = std::min(resolution * clock_cost_estimation_tick_limit, FloatDuration<Clock>(clock_cost_estimation_time_limit));
                auto time_clock = [](int k) {
                    return Detail::measure<Clock>([k] {
                        for (int i = 0; i < k; ++i) {
                            volatile auto ignored = Clock::now();
                            (void)ignored;
                        }
                    }).elapsed;
                };
                time_clock(1);
                int iters = clock_cost_estimation_iterations;
                auto&& r = run_for_at_least<Clock>(std::chrono::duration_cast<ClockDuration<Clock>>(clock_cost_estimation_time), iters, time_clock);
                std::vector<double> times;
                int nsamples = static_cast<int>(std::ceil(time_limit / r.elapsed));
                times.reserve(nsamples);
                std::generate_n(std::back_inserter(times), nsamples, [time_clock, &r] {
                    return static_cast<double>((time_clock(r.iterations) / r.iterations).count());
                });
                return {
                    FloatDuration<Clock>(mean(times.begin(), times.end())),
                    classify_outliers(times.begin(), times.end()),
                };
            }

            template <typename Clock>
            Environment<FloatDuration<Clock>> measure_environment() {
                static Environment<FloatDuration<Clock>>* env = nullptr;
                if (env) {
                    return *env;
                }

                auto iters = Detail::warmup<Clock>();
                auto resolution = Detail::estimate_clock_resolution<Clock>(iters);
                auto cost = Detail::estimate_clock_cost<Clock>(resolution.mean);

                env = new Environment<FloatDuration<Clock>>{ resolution, cost };
                return *env;
            }
        } // namespace Detail
    } // namespace Benchmark
} // namespace Catch

#endif // TWOBLUECUBES_CATCH_DETAIL_ESTIMATE_CLOCK_HPP_INCLUDED