Function estimateClockResolution

tests/catch.hpp:12036–12064

    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();