ashley at semantic.org
Mon Jan 31 08:03:52 EST 2005
In article <41FE23F1.6080908 at cql.com>, Seth Kurtzberg <seth at cql.com>
> Doesn't automatically forcing a system clock tick screw up the time?
Well, one nanosecond is three cycles of a 3GHz processor. For the time
being it seems unlikely to be a problem.
> Also, what happens when you are using NTP? NTP might just correct it,
> but it would screw up the calculations NTP uses and it could start
NTP knows all about this, and it's only an issue with leap seconds. See
> I don't think we disagree, in general, it's more a question of whether
> or not system clock related computations should match the precision of
> the system clock. 123.45000 implies that the value is known to be
> accurate to five decimal points (just picking an arbitrary number of
> digits beyond the decimal point, because I don't recall the actual
> precision of the high resolution library). Truncating at the end is
> also not "correct," because the final result in general might be
> different if you compute with five digits and truncate, rather than
> computing with two digits throughout. (Again, whatever the number is; I
> pulled 2 digit out of the air, just to use a number.)
> To me all this shows that the system clock needs to be handled as a
> special case, not just converted into the high resolution representation
The system clock gives measurements with a particular accuracy attached.
This isn't a particularly special case, other time applications may
involve measurements or calculations to some particular accuracy.
Ashley Yakeley, Seattle WA
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