[tz] So, about those LMT offsets
Paul Eggert
eggert at cs.ucla.edu
Mon May 24 02:59:13 UTC 2021
On 5/23/21 2:43 PM, Clive D.W. Feather via tz wrote:
> there
> should be a way to put a "not valid before" marker into the zone data and
> have the functions return either an error or a clearly nonsense answer.
RFC 8536 section 5.1 says that client code can use the first transition
time as a "not valid before" marker - that is, client code can return an
error before the first transition.
However, it's common for clients to assume that all timestamps can be
converted - something that is true on older or smaller POSIX hosts with
32-bit time_t and 32-bit int - and so tzcode (and all POSIXish client
code that I know about) does convert timestamps before the first
transition. And when doing that conversion, using the LMT offset
typically yields a more-accurate answer for the affected area than using
a 0 offset would. I doubt whether we could change this behavior in
client code now, without causing more trouble than it'd cure.
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