Ticket #11660: stable_get_last_bootup_time.hpp

inline ULONGLONG stable_precision(ULONGLONG value)
{
    static const ULONGLONG precision = 64;
    ULONGLONG remainder = value % precision;
    ULONGLONG truncated = value - remainder;
    ULONGLONG offset = (remainder >= (precision / 2)) ? precision : 0;
    ULONGLONG stable = truncated + offset;
    return stable;
}

inline bool get_last_bootup_time(std::string &stamp)
{
    ULONGLONG t0 = 0;
    ULONGLONG t1 = 1;
    SYSTEMTIME st;
    ZeroMemory(&st, sizeof(st));

    static const size_t max_attempts = 113; // Limit number of retries to arbitrary number (not infanite) but suficiently large enough to acomplish timing except in pedantic cases...
    for (size_t i = 0; (i != max_attempts) && (t0 != t1); ++i)
    {
        t0 = GetTickCount64();
        GetSystemTime(&st);
        t1 = GetTickCount64();
    }
    if (t0 != t1)
        return false; // Presume this is *very* unlikely.

    // Convert system time (Y/M/D h/m/s/millisec) to file time (100 nanosecond intervals).
    FILETIME ft;
    if (SystemTimeToFileTime(&st, &ft) == FALSE)
        return false; // Presume this will never fail since system time is expected to be valid.

    ULARGE_INTEGER uli;
    uli.LowPart = ft.dwLowDateTime;
    uli.HighPart = ft.dwHighDateTime;

    // Convert file time to milliseconds.
    ULONGLONG ft_millisec = uli.QuadPart / 10000;

    // Round milliseconds to the nearest stable precision (inconsistency/imprecision between system clock & tick count).
    ULONGLONG time = stable_precision(ft_millisec);
    ULONGLONG ticks = stable_precision(t0);
    ULONGLONG boot_time = time - ticks;
    std::ostringstream oss;
    oss << boot_time;
    stamp = oss.str();

    return true;
}