Catch2/src/catch2/catch_timer.cpp

//              Copyright Catch2 Authors
// Distributed under the Boost Software License, Version 1.0.
//   (See accompanying file LICENSE_1_0.txt or copy at
//        https://www.boost.org/LICENSE_1_0.txt)

// SPDX-License-Identifier: BSL-1.0
#include <catch2/catch_timer.hpp>

#include <chrono>

static const uint64_t nanosecondsInSecond = 1000000000;

namespace Catch {

    auto getCurrentNanosecondsSinceEpoch() -> uint64_t {
        return std::chrono::duration_cast<std::chrono::nanoseconds>( std::chrono::high_resolution_clock::now().time_since_epoch() ).count();
    }

    namespace {
        auto estimateClockResolution() -> uint64_t {
            uint64_t sum = 0;
            static const uint64_t iterations = 1000000;

            auto startTime = getCurrentNanosecondsSinceEpoch();

            for( std::size_t i = 0; i < iterations; ++i ) {

                uint64_t ticks;
                uint64_t baseTicks = getCurrentNanosecondsSinceEpoch();
                do {
                    ticks = getCurrentNanosecondsSinceEpoch();
                } while( ticks == baseTicks );

                auto delta = ticks - baseTicks;
                sum += delta;

                // If we have been calibrating for over 3 seconds -- the clock
                // is terrible and we should move on.
                // TBD: How to signal that the measured resolution is probably wrong?
                if (ticks > startTime + 3 * nanosecondsInSecond) {
                    return sum / ( i + 1u );
                }
            }

            // We're just taking the mean, here. To do better we could take the std. dev and exclude outliers
            // - and potentially do more iterations if there's a high variance.
            return sum/iterations;
        }
    }
    auto getEstimatedClockResolution() -> uint64_t {
        static auto s_resolution = estimateClockResolution();
        return s_resolution;
    }

    void Timer::start() {
       m_nanoseconds = getCurrentNanosecondsSinceEpoch();
    }
    auto Timer::getElapsedNanoseconds() const -> uint64_t {
        return getCurrentNanosecondsSinceEpoch() - m_nanoseconds;
    }
    auto Timer::getElapsedMicroseconds() const -> uint64_t {
        return getElapsedNanoseconds()/1000;
    }
    auto Timer::getElapsedMilliseconds() const -> unsigned int {
        return static_cast<unsigned int>(getElapsedMicroseconds()/1000);
    }
    auto Timer::getElapsedSeconds() const -> double {
        return getElapsedMicroseconds()/1000000.0;
    }


} // namespace Catch