include/internal/benchmark/detail/catch_run_for_at_least.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)
 */

// Run a function for a minimum amount of time

#ifndef TWOBLUECUBES_CATCH_RUN_FOR_AT_LEAST_HPP_INCLUDED
#define TWOBLUECUBES_CATCH_RUN_FOR_AT_LEAST_HPP_INCLUDED

#include "../catch_clock.hpp"
#include "../catch_chronometer.hpp"
#include "catch_measure.hpp"
#include "catch_complete_invoke.hpp"
#include "catch_timing.hpp"
#include "../../catch_meta.hpp"

#include <utility>
#include <type_traits>

namespace Catch {
    namespace Benchmark {
        namespace Detail {
            template <typename Clock, typename Fun>
            TimingOf<Clock, Fun(int)> measure_one(Fun&& fun, int iters, std::false_type) {
                return Detail::measure<Clock>(fun, iters);
            }
            template <typename Clock, typename Fun>
            TimingOf<Clock, Fun(Chronometer)> measure_one(Fun&& fun, int iters, std::true_type) {
                Detail::ChronometerModel<Clock> meter;
                auto&& result = Detail::complete_invoke(fun, Chronometer(meter, iters));

                return { meter.elapsed(), std::move(result), iters };
            }

            template <typename Clock, typename Fun>
            using run_for_at_least_argument_t = typename std::conditional<is_callable<Fun(Chronometer)>::value, Chronometer, int>::type;

            struct optimized_away_error : std::exception {
                const char* what() const noexcept override {
                    return "could not measure benchmark, maybe it was optimized away";
                }
            };

            template <typename Clock, typename Fun>
            TimingOf<Clock, Fun(run_for_at_least_argument_t<Clock, Fun>)> run_for_at_least(ClockDuration<Clock> how_long, int seed, Fun&& fun) {
                auto iters = seed;
                while (iters < (1 << 30)) {
                    auto&& Timing = measure_one<Clock>(fun, iters, is_callable<Fun(Chronometer)>());

                    if (Timing.elapsed >= how_long) {
                        return { Timing.elapsed, std::move(Timing.result), iters };
                    }
                    iters *= 2;
                }
                throw optimized_away_error{};
            }
        } // namespace Detail
    } // namespace Benchmark
} // namespace Catch

#endif // TWOBLUECUBES_CATCH_RUN_FOR_AT_LEAST_HPP_INCLUDED