Re: timestamp resolution

[Hans Aberg]

On 4 May 2007, at 07:25, Larry Dwyer wrote:
> At 07:21 PM 5/3/2007, address@hidden wrote:
> > > Having a clock number implies that the clock can be used with
> > > clock_gettime() or even timer_create().  There is no reason to  
> > assume
> > > that there is such a clock available.
> >
> > However, if there is such a clock available, being able to call
> > clock_gettime() on it is a *good* thing.  In those cases (such as a
> > network filesystem) where it is not available, clock_gettime() can
> > always return an error.
>
> As Ulrich points out, an implementation would need a unique  
> clock_id for each file system it supports.  Even if this was  
> considered a reasonable solution, we would have to invent a new  
> function, or reuse pathconf(..), to associate the particular  
> clock_id value that corresponds to a particular filesystem.

I haven't followed this discussion too closely, but I think one of  
the best ways to count (calendar) time is using the Julian period  
used by astronomers:
  http://en.wikipedia.org/wiki/Julian_day

It sets the epoch (time 0.0) to noon UT (Universal Time), January 1,  
-4712 (= 4713 BC, as the astronomical year 0 = 1 BC). Calendar  
conversions are easy. (The number of seconds since that date requires  
38 bits, I got it to.)

Systems that uses a different epoch, merely needs to indicate the  
time offset.


On 4 May 2007, at 00:20, James Youngman wrote:

> I can't think offhand of an exception.  The difference between the
> MS-DOS epoch and the Unix epoch is evenly divisible by 2 seconds (I
> think; though there were 9 leap seconds in the 1970s, hmm...).  But
> might there be an exception I can't immediately recall?  Quite
> probably.

This would also resolve problems with leap seconds: just do what UT  
does. There is a proposal to scrap the leap seconds in favor of leap  
hours, in which case one only needs to take into account the leap  
seconds introduced so far, as it takes a couple of thousand years  
until the first leap hour comes by.

  Hans Aberg