Markus Kuhn Markus.Kuhn at
Sun Oct 4 11:03:49 UTC 1998

"D. J. Bernstein" wrote on 1998-10-03 04:39 UTC:
> Markus Kuhn writes:
> > The best atomic clock on this planet (CS1 by PTB in Braunschweig) barely
> > can do UTC with a real-time precision of one nanosecond.
> There are many scientific projects for which nanosecond resolution is
> inadequate. ``It's the intervals, stupid.''

I don't see, how the standard C time API would be related to any of
these applications. You would use in these scientific applications
special purpose instrumentation with special purpose control software
that does not even touch the C time API. We are not trying to solve any
problem related in any way to any kind of time, we are just trying to
define a robust interface to the clock information available to a good
operating system on a wide range of general-purpose computers. Tell me
some real-world examples where subnanoseconds play a role in
applications running on general-purpose computers and where access to
operating system clocks and timezone databases is required with
subnanosecond resolution to convince me instead of calling me
``stupid''. I am somewhat familiar with radio-astronomy instrumentation
and requirements for VLBI, but I have extreme difficulties to imagine
that this subnanosecond data would be processed through the
general-purpose C API and I see absolutely no need to extend it. I am
convinced that nanosecond resolution provides a very comfortable safety
margin to the resolution actually required by C applications from the
standard library. You certainly do not measure the position of your
radio telescope with 3 cm precision (0.1 ns) by performing time request
calls to your C API! You would use external picosecond hardware phase
comparators clocked by caesium time normals, which send you the data as
ASCII floating point numbers for further processing in your Fortran
tools (all available from Hewlett Packard for a few kilodollars for the
advanced hobby radio astronomer).


Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK
email: mkuhn at,  home page: <>

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