While "3...2...1...leap" was mentioned on the mailing list in 1998, support for rolling leap seconds goes all the way back to the 1.1, 1988-01-25 version of the leapseconds file (included below). Folks looking for documentation of "3...2...1...leap" in New York might focus on 1987 or, before that, 1972 through 1979. (My guess 1987.) --ado # @(#)leapseconds 1.1 # Allowance for leapseconds added to each timezone file. # The correction (+ or -) is made at the given time, so lines # will typically look like: # Leap YEAR MON DAY 23:59:60 + R/S # or # Leap YEAR MON DAY 23:59:59 - R/S # If the leapsecond is Rolling (R) the given time is local time # If the leapsecond is Stationary (S) the given time is GMT # Leap YEAR MONTH DAY HH:MM:SS CORR R/S Leap 1972 Jun 30 23:59:60 + S Leap 1972 Dec 31 23:59:60 + S Leap 1973 Dec 31 23:59:60 + S Leap 1974 Dec 31 23:59:60 + S Leap 1975 Dec 31 23:59:60 + S Leap 1976 Dec 31 23:59:60 + S Leap 1977 Dec 31 23:59:60 + S Leap 1978 Dec 31 23:59:60 + S Leap 1979 Dec 31 23:59:60 + S Leap 1981 Jun 30 23:59:60 + S Leap 1982 Jun 30 23:59:60 + S Leap 1983 Jun 30 23:59:60 + S Leap 1985 Jun 30 23:59:60 + S Leap 1987 Dec 31 23:59:60 + S On Mon, Sep 13, 2021 at 3:57 AM Guy Harris <gharris@sonic.net> wrote:
On Sep 13, 2021, at 12:18 AM, Paul Eggert via tz <tz@iana.org> wrote:
Thanks for the background.
You participated in the tz mailing list thread:
http://mm.icann.org/pipermail/tz/1998-May/010164.html
in which he mentioned that back in 1998:
http://mm.icann.org/pipermail/tz/1998-May/010159.html
(things I learned from a Web search today; no, I didn't remember that discussion, either).
(And, on one of the topics you addressed in your message:
What Epoch do systems that use leap seconds use?
In practice, such systems define 1972-01-01 00:00:00Z == (time_t) 63072000, i.e. it's as if there were no leap seconds before 1972.
Presumably systems that *don't* use leap seconds use the same definition.)