template <typename T> int sgn(T val) {
    return (T(0) < val) - (val < T(0));
}

std::vector<std::pair<double, double>> find_intervals(double from, double to, double step) {
    std::vector<std::pair<double, double>> roots;
    std::pair<double, double> p;
    double x1, x2;
    x1 = from;
    x2 = x1 + step;
    while (x2 < to) {
        if (sgn(f(x1)) != sgn(f(x2))) {
           p.first = x1;
           p.second = x2;
           roots.emplace_back(p);
           std::cout << "found interval from " << x1 << " to " << x2 << std::endl;
        }
        x1 = x2;
        x2 += step;
    }

    return roots;
}