Re: GPS Leap Second Scheduled!

[Feuer <feuer@his.com>]

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H. Peter Anvin wrote:

> Followup to:  <199809092149.RAA06993@hilfy.ece.cmu.edu>
> By author:    "Brandon S. Allbery KF8NH" <allbery@kf8nh.apk.net>
> In newsgroup: linux.dev.kernel
> >
> > In message <19980909200032.B13292@caffeine.ix.net.nz>, Chris Wedgwood writes:
> > +-----
> > | On Wed, Sep 09, 1998 at 12:59:47AM +0000, H. Peter Anvin wrote:
> > | > The way xntp deals with leap seconds is it lets the epoch float...
> > | > i.e. it holds time_t to the same value for two seconds.
> > | Cool... so 1970 becomes even longer ago that I would have assumed
> > | then?
> > +--->8
> >
> > That's the only semi-reasonable (I stress *semi-*) interpretation one can
> > give to the current standard.  The other possibilities are worse.
> >
>
> Right.  I think the right solution is one I suggested on c.o.l.d.s
> recently:
>
> - time_t being a 64-bit signed integer linked to UTC
> - struct timespec (and struct timeval, presumably) having an extra
>   field added:
>
>         64-bit seconds field (same as time_t) linked to UTC
>         32-bit nanosecond field (microsecond for timeval) linked to TAI
>         32-bit integral TAI-UTC difference
>
> That way any moment in time will be uniquely derivable at least, at a
> positive leap second, you will see the progression (where T means a
> time_t value divisible by 86400):
>  

Why would you have the TAI-UTC difference instead of just TAI?
The part of your message below was very confusing to me.
 
 

>  
>         tv_sec          tv_delta        UTC
>
>         T-3             N               23:59:57
>         T-2             N               23:59:58
>         T-1             N               23:59:59
>         T-1             N+1             23:59:60
>         T               N+1             00:00:00
>         T+1             N+1             00:00:01
>         T+2             N+1             00:00:02
>
> ... and for a negative leap second ...
>
>         tv_sec          tv_delta
>
>         T-3             N               23:59:57
>         T-2             N               23:59:58
>         T               N-1             00:00:00
>         T+1             N-1             00:00:01
>         T+2             N-1             00:00:02
>
> We may want to have a testable bit that we're "in" a leap second for
> the 23:59:60 case...
>
>         -hpa
>
> --
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