[tz] leapseconds.awk, LEAP directives and references

[Arthur David Olson]

> Perhaps Arthur David Olson or Bradley White can take a look at this, as
they're the leap second gurus for tz.
> I've never tested negative leap seconds.

Using 23:59:59 for a negative leap second seems to do the right thing, as
witness the typescript at the bottom of this message.

    @dashdashado

Script started on Fri, Apr 7, 2017 2:37:27 PM

$ grep 2020 leapseconds
Leap	2020	Jun	30	23:59:59	-	S
$ make install TOPDIR=$PWD/tmp REDO=right_only >&-
$ ./zdump -v America/New_York | grep 2020
America/New_York  Sun Mar  8 06:59:59 2020 UT = Sun Mar  8 01:59:59
2020 EST isdst=0 gmtoff=-18000
America/New_York  Sun Mar  8 07:00:00 2020 UT = Sun Mar  8 03:00:00
2020 EDT isdst=1 gmtoff=-14400
America/New_York  Tue Jun 30 23:59:58 2020 UT = Tue Jun 30 19:59:58
2020 EDT isdst=1 gmtoff=-14400
America/New_York  Wed Jul  1 00:00:00 2020 UT = Tue Jun 30 20:00:00
2020 EDT isdst=1 gmtoff=-14400
America/New_York  Sun Nov  1 05:59:59 2020 UT = Sun Nov  1 01:59:59
2020 EDT isdst=1 gmtoff=-14400
America/New_York  Sun Nov  1 06:00:00 2020 UT = Sun Nov  1 01:00:00
2020 EST isdst=0 gmtoff=-18000
$ exit
exit
Script done on Fri, Apr  7, 2017  2:38:11 PM


On Tue, Apr 4, 2017 at 6:33 PM, Paul Eggert <eggert at cs.ucla.edu> wrote:

> On 04/04/2017 09:02 AM, Chris Woodbury via tz wrote:
>
>> I reviewed the C code and, it seems to me, the transaction
>> added should actually be for the second before, 23:59:58,
>> as the transaction itself causes 23:59:59 to be skippedaltogether.
>>
>
> Perhaps Arthur David Olson or Bradley White can take a look at this, as
> they're the leap second gurus for tz. I've never tested negative leap
> seconds.
>
> Also, I've an AWK script that uses the IERS file Leap_Seconds.dat
>> rather than the NIST leap-seconds.listfile.
>>
>
> Although that would be a better technical solution, in the past we've
> shied away from it because the IERS file is copyrighted and we and we and
> our downstream users don't clearly have permissions to copy and
> redistribute it.
>
>
> USNO MAIA also has straight list
>> of leap-seconds in a different format. <http://maia.usno.navy.mil/ser
>> 7/leapsec.dat>
>>
>
> Thanks, I was not aware of this file. It is public-domain, so perhaps we
> could use it. Is it updated in a timely fashion when new IERS bulletins are
> published? And is that web server highly available? These have been
> sticking points for the NIST file.
>
> Another good, comprehensive article is "The leap second: its history
>> and possible future" by R.A. Nelson, et al, from Metrogia Vol 38,
>> pp. 509-529 (2001).  PDF available (with permission) at:
>>
>> <https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf>
>>
>
> Yes, we link to that in tz-link.htm.
>
>
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