"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 -- Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK email: mkuhn at acm.org, home page: <http://www.cl.cam.ac.uk/~mgk25/>