[tz] isdst bug Europe/Dublin (tzdb-2019c)

[Clive D.W. Feather]

Guy Harris said:
>>     The notation of values of TAI using the Gregorian calendar is helpful
>>     when comparing time scales.
> 
> So how is that defined?
> 
> Do you just take a UTC value for the same instant, add the current TAI - UTC delta to it - and, for overflow (meaning "resulting seconds > 59 or minutes > 59 or...), "carry into" the calendar date, so that an event that took place at the end of 2018, with a UTC label, took place at the beginning of 2019, with a TAI label?

No.

You take a Gregorian calendar (by default; in principle you could use
Julian or something else) and use it to count *all* SI seconds, so that
every day has exactly 86400 seconds in it. It works the same way as UT1,
but without the unpredictable-length "seconds".

You can convert that to UTC by subtracting the relevant (not "current")
TAI-UTC delta and doing correct carries, remembering to handle the edge
cases when the delta changes.

-- 
Clive D.W. Feather          | If you lie to the compiler,
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