Function bench

src/Tests/CoolProp-Tests-TermCacheProfile.cpp:190–213

// Run `n_trials` of `reps` repetitions of `fn`, return mean and stddev of ns/iter.
template <typename F>
TrialStats bench(F&& fn, std::size_t reps, std::size_t n_trials) {
    std::vector<double> ns_per_iter;
    ns_per_iter.reserve(n_trials);
    volatile double sink = 0.0;
    for (std::size_t t = 0; t < n_trials; ++t) {
        const auto t0 = std::chrono::steady_clock::now();
        for (std::size_t r = 0; r < reps; ++r) {
            sink = sink + fn();
        }
        const auto t1 = std::chrono::steady_clock::now();
        const double dt_ns = std::chrono::duration<double, std::nano>(t1 - t0).count();
        ns_per_iter.push_back(dt_ns / static_cast<double>(reps));
    }
    (void)sink;
    double sum = 0.0;
    for (double x : ns_per_iter)
        sum += x;
    const double mean = sum / static_cast<double>(n_trials);
    double sq = 0.0;
    for (double x : ns_per_iter)
        sq += (x - mean) * (x - mean);
    const double stddev = (n_trials > 1) ? std::sqrt(sq / static_cast<double>(n_trials - 1)) : 0.0;
    return TrialStats{mean, stddev};
}

// Pick a representative single-phase (T, p) state for each benchmark fluid, run the
// AbstractState through update so tau/delta are well-defined, then return log(tau)