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

Paul Eggert eggert at cs.ucla.edu
Wed Dec 11 18:39:07 UTC 2019

On 12/11/19 10:12 AM, Michael H Deckers wrote:
>     the tzdb description in
>     newctime.3 ... guaranteed (in addition to what C and POSIX require)
>     that
>        "Tm_isdst is non-zero if summer time is in effect"
>     and probably the "if" was even meant as "if and only if".

I don't think that old wording was ever intended to mean that tm_isdst 
was to be set only in summer, or even only in daylight-saving periods 
that were used in summer and adjacent time periods. Such a meaning would 
have been contradicted by longstanding data, such as Belize's observance 
of DST from October through February in late 1918 through early 1943.

Instead, it was merely sloppy wording where "summer time" was 
incorrectly used as a synonym for "daylight saving time", the wording 
that is in the relevant standards and that corresponds to the 
abbreviation "tm_isdst".

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