How to get NSTimeInterval value from last boot

Question

I need to get NSTimeInterval value from last device boot. I found CACurrentMediaTime() which suits this task, but in my app I am not using Core Animation and I don\'t think

Answer 1

The fastest low-level method is to read system uptime from processor using mach_absolute_time()

#include 

int systemUptime()
{
    static float timebase_ratio;

    if (timebase_ratio == 0) {
       mach_timebase_info_data_t s_timebase_info;
       (void) mach_timebase_info(&s_timebase_info);

       timebase_ratio = (float)s_timebase_info.numer / s_timebase_info.denom;
    }

    return (int)(timebase_ratio * mach_absolute_time() / 1000000000);
}

Note that timebase_ratio is different for processors. For example, on macbook it equals 1 whereas on iPhone 5 it equals 125/3 (~40).