Tagging timestamps; "proleptic"
cowan at locke.ccil.org
Wed Oct 7 15:57:48 UTC 1998
Markus Kuhn wrote:
> Note that there is no reason for the tagging to show up in the bits of
> the value. The tagging can be done implicitly by naming your variables
> in software such that they make clear whether they are intended for UTC
> or TAI or whatever values.
It is not *necessary* for the timestamp-type to appear in the timestamp,
but doing so costs only a few bits and provides an excellent
defensive programming mechanism: it prevents you from attempting to
convert TAI timestamps to the local timezone, a meaningless activity.
> Question: What precisely does "proleptic" mean and where is it defined.
> The most official definition of the Gregorian calendar that I have to
> reference is ISO 8601, and it does not use the term "proleptic". My time
> and astronomy references to not define the term either.
The WWWebster dictionary defines "prolepsis" as:
anticipation: the representation or assumption of
a future act or development as if presently existing
or accomplished [...]
"Proleptic" would be the standard adjectival form. The HP MPE/ix
documentation (http://jazz.external.hp.com/src/year2000/dateintr.txt) says:
# All the date intrinsics follow what is called the "Proleptic Calendar".
# Stated in simple terms this calendar ignores the fact that calendars in
# different countries changed at different times (around the year 1753) .
# In other words, there are no lost days and there is no year 0. This is
# similar to the calendar used by ALLBASE/SQL date/time functions.
The Julian Day count is based on a "proleptic Julian calendar", i.e.
the Julian calendar as if it was in use from 4713 B.C.E. to the
John Cowan http://www.ccil.org/~cowan cowan at ccil.org
You tollerday donsk? N. You tolkatiff scowegian? Nn.
You spigotty anglease? Nnn. You phonio saxo? Nnnn.
Clear all so! 'Tis a Jute.... (Finnegans Wake 16.5)
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