Generalized function evaluation

#include <type_traits>
#include <utility>

// functions, functors, lambdas, etc.
template<
    class F, class... Args,
    class = typename std::enable_if<!std::is_member_function_pointer<F>::value>::type,
    class = typename std::enable_if<!std::is_member_object_pointer<F>::value>::type
    >
auto eval(F&& f, Args&&... args) -> decltype(f(std::forward<Args>(args)...))
{
    return f(std::forward<Args>(args)...);
}

// const member function
template<class R, class C, class P, class... Args>
auto eval(R(C::*f)() const, P&& p, Args&&... args) -> R
{
    return (*p.*f)(std::forward<Args>(args)...);
}

template<class R, class C, class... Args>
auto eval(R(C::*f)() const, C& c, Args&&... args) -> R
{
    return (c.*f)(std::forward<Args>(args)...);
}

// non-const member function
template<class R, class C, class P, class... Args>
auto eval(R(C::*f)(), P&& p, Args&&... args) -> R
{
    return (*p.*f)(std::forward<Args>(args)...);
}

// member object
template<class R, class C>
auto eval(R(C::*m), const C& c) -> const R&
{
    return c.*m;
}

template<class R, class C>
auto eval(R(C::*m), C& c) -> R&
{
    return c.*m;
}

Taken from here: http://functionalcpp.wordpress.com/2013/08/03/generalized-function-evaluation/

Quick stablize NTP

By design NTP converges on the correct time slowly so as to prevent jumps in the clock time. It achieves this by varying the frequency of the clock rather than stepping the time.

When the clock is far out (say, after a reboot when the hardware clock isn't sync'd with the system clock), overshoot is caused because NTP applies a huge frequency correction to accelerate the convergence between the kernel clock time and the real time.

Overshoot causes the clock to oscillate, eventually settling down to the correct time and stabilizing.

If we want to quickly stabilize NTP we can apply the following process:

1. Stop NTP - /etc/init.d/ntp stop
2. Reset kernel bias - /usr/sbin/ntptime -f 0
3. Run ntpdate to sync the time - ntpdate -p8 <server>
4. Run it several times, this will make more measurements and have the kernel get a more accurate idea of the time
5. Start NTP - /etc/init.d/ntp start