Benchmarking utilities

benchmark.cpp

struct timeit {
    decltype(chrono::high_resolution_clock::now()) begin;
    const string label;
    timeit(string label = "???") : label(label) { begin = chrono::high_resolution_clock::now(); }
    ~timeit() {
        auto end = chrono::high_resolution_clock::now();
        auto duration = chrono::duration_cast<chrono::milliseconds>(end - begin).count();
        cerr << duration << "ms elapsed [" << label << "]" << endl;
    }
};