Time Libraries Rough Draft

Keith Wansbrough Keith.Wansbrough at cl.cam.ac.uk
Fri Feb 11 06:03:54 EST 2005

Seth wrote:

> I want to compute the correct interval between two timestamps.  I guess 
> I not only don't see why it's impossible, I don't even see why it is 
> difficult.  The difficulty, if it exists, comes from converting the 
> absolute time into calendar time, but even that isn't really difficult.  
> The firmware in a GPS receiver does it.  So it is clearly not impossible.

The firmware in a GPS receiver can tell you the _current_ time, in
both TAI and UTC, because it is continually receiving signals from the
satellite containing the pair (TAI_time,UTC_offset).  If the satellite
says (n,m), then it reports n as the TAI time, and n+m as the UTC

The Haskell time library will (a) not have access to a continuous
stream of information from the GPS satellites, and (b) be asked to
convert TAI to UTC at times other than the current time.  The above
GPS receiver behaviour (i.e., implementation of the "+" function)
doesn't make it any more possible for System.Time to do the Right

--KW 8-)

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