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The inverse lookup compared the TT-shifted ns count against UTC leap-second thresholds, so instants within the leap offset before each threshold read back one second early. A TT2000 inside an inserted leap second now maps onto the following UTC second, as cdflib does.
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UTC -> TT2000 is injective, TT2000 -> UTC folds each inserted leap second
onto the following second, so mixed comparisons and differences are done
in the CDF type. Timestamp{Nanosecond} (Durations.jl) backs TT2000
parsing, printing and calendar fields; Epoch and Epoch16 span years
0-9999 and keep DateTime for those.
Also: comparison across CDF epoch types, Epoch16 ordering and
Epoch16 ± Period, Date/Time/days accessors, TT2000(::DateTime) up to
2292, leap-second lookup on the nanosecond count (crashed just below
1972), ISTP FILLVAL display for TT2000 and Epoch16.
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Two commits.
fix: TT2000 to DateTime off by 1 s before each leap second. The inverse lookup compared the TT-shifted count against UTC leap-second thresholds, so for the ~30 s before each leap second since 1972, reads came back 1 s early (e.g.
DateTime(TT2000(DateTime("2016-12-31T23:59:30")))gave23:59:29). Regression values come fromcdflib.cdfepoch.compute_tt2000.feat!: promote DateTime/Timestamp to the CDF epoch types (adds Durations.jl 1.4 for
Timestamp).Date,DateTimeandTimestamppromote toTT2000/Epoch16/Epochrather than the epoch promoting toDateTime. UTC -> TT2000 is injective, while TT2000 -> UTC folds each inserted leap second onto the following second, so comparing in UTC would equate distinct instants and under-count differences across a leap second. A TT2000 0.4 ms afterDateTime(2020)no longer compares==to it.Timestamp{P}(x)/convert(Timestamp{P}, x)for all CDF epochs.TT2000parses, prints and exposes calendar fields to the nanosecond throughTimestamp{Nanosecond}.EpochandEpoch16span years 0-9999, beyondTimestamp{Nanosecond}(1677-2262), and keepDateTimefor calendar fields and printing.DateTime(x)for TT2000/Epoch16 floors to the millisecond (Epoch16 used to round).Epoch16ordering and± Period;Date,Timeand day-based accessors.Fixes found while probing:
DateTimethrew for instants within 0.5 ms before 1972-01-01 and used the next day's offset within 0.5 ms before earlier midnights.TT2000(::DateTime)covers the full TT2000 range (to 2292).FILLVALdisplay: TT2000 uses the ISTP fill (typemin(Int64)) rather than9999; the Epoch16 fill no longer throws.Known limits: comparing a TT2000 with a
DateTimeoutside the TT2000 range throws;stringof a TT2000 in 2262-2292 throws;floorof an instant inside a leap second lands on the following second.Breaking (promotion and equality semantics). CDFDatasets' tests pass locally against this branch; downstream compat needs widening on release.