Question

Apple has extremely comprehensive documentation, but I can’t find any documentation for the function AbsoluteToNanoseconds? I was to find the difference between AbsoluteToNanoseconds and AbsoluteToDuration.

Note

I am beginning to think that the Apple Docs only cover Objective-C functions? Is this the case?

I found the following by using Apple-double-click:

Duration 32-bit millisecond timer for drivers
AbsoluteTime 64-bit clock

Answer 1

I’m not sure why it isn’t documented anywhere, but here is an example of how it is used, if that helps:

static float HowLong(
    AbsoluteTime endTime,
    AbsoluteTime bgnTime
    )
{
    AbsoluteTime absTime;
    Nanoseconds  nanosec;

    absTime = SubAbsoluteFromAbsolute(endTime, bgnTime);
    nanosec = AbsoluteToNanoseconds(absTime);
    return (float) UnsignedWideToUInt64( nanosec ) / 1000.0;
}

UPDATE:

“The main reason I am interested in the docs is to find out how it differs from AbsoluteToDuration”

That’s easier. AbsoluteToNanoseconds() returns a value of type Nanoseconds, which is really an UnsignedWide struct.

struct UnsignedWide {
  UInt32              hi;
  UInt32              lo;
};

In contrast, AbsoluteToDuration() returns a value of type Duration, which is actually an SInt32 or signed long:

typedef SInt32 Duration;

Durations use a smaller, signed type because they are intended to hold relative times. Nanoseconds, on the other hand, only make sense as positive values, and they can be very large, since computers can stay running for years at a time.