On Mon, 11 Mar 2019 at 18:30, Paul Eggert <eggert@cs.ucla.edu> wrote:
On 3/11/19 4:18 AM, Christopher Wong wrote:
Is it correct that the switch between LMT to GMT is set to the specified start of the time range?
Yes. If you tell zic's new -r option to discard info for timestamps before time T, then the first transition in the output TZif file will be at time T. This is so that a TZif reader can determine the range of timestamps that the TZif file covers. See Internet RFC 8536 section 5.1.
Yes, but in the examples given which truncate from 1977 and 1984, that shouldn't be a transition from LMT, as LMT was not observed in that Zone since 1912: "As with untruncated TZif files, time type 0 indicates local time immediately before the start point, and the time type of the first transition indicates local time thereafter." So if my truncation range starts with POSIX timestamp N, I would expect time type zero to correctly and accurately represent timestamp N−1 (though, of course, not necessarily N−2 or any earlier). In each of these examples, that's GMT, not LMT. The file would then have the required transition at time N, though in these cases, that would be a no-op transition to the same time type, as it's still GMT. -- Tim Parenti