On Mon, 12 Jan 2009, ChrisK wrote:
Lennart is right that 1 picosecond accuracy is absurd compared to all the jitters and drifts in anything but an actual atomic clock in your room. But since CPUs tick faster than nanosecond the CPUTime needs better than 1 nanosecond granularity. I agree with Lennart — I also want an Integral type; it keeps the granularity constant and avoids all the pitfalls of doing math with a Double. Out of simplicity I can see why the granularity was set to 1 picosecond as it is slightly easier to specify than 100 picosecond or 10 picosecond or 1/60 nanosecond (hmmm... arcnanosecond?).
The FreeBSD kernel uses a 64+64 bit fixed point type to represent time,
where the integer part is a normal Unix time_t. The fractional part is
64 bits wide in order to be able to represent multi-GHz frequencies
precisely.
http://phk.freebsd.dk/pubs/timecounter.pdf
Tony.
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f.anthony.n.finch