[Octave-bug-tracker] [bug #53910] Documentation of Leap Seconds

[Ian McCallion]

URL:
  <http://savannah.gnu.org/bugs/?53910>

                 Summary: Documentation of Leap Seconds
                 Project: GNU Octave
            Submitted by: ianmcc
            Submitted on: Tue 15 May 2018 01:57:06 PM UTC
                Category: Documentation
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Documentation
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.4.0
        Operating System: Any

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Details:

The only reference to Leap seconds in the Octave documentation at present is
under the datenum function, which says:

Warning: leap seconds are ignored. A table of leap seconds is available on the
Wikipedia entry for leap seconds.

What "ignored" means, and what the implications are of ignoring leap seconds.
should be spelled out better. I propose something like the following:

36.x Leap Seconds

>From time to time leap seconds are added in order to keep atomic clock time,
TAI, and earth time, UTC0, in sync. Hence some days will have 86401 seconds
rather than 86400. This is how the situation is handled:

- All Octave date time functions assume that every day is 86400 seconds.

- The octave time() function uses underlying system timing services which may
or may not return a time representing the 86401th second of the day. 

- Interval timing (t=time();do something; interval=time-t;) may be affected
when a leap second is inserted. At one extreme the final second of the day may
last two seconds, and at the other the system clock may be slowed down
fractionally for hours before and after the leap second in order to avoid
perceptible glitches.

If this might matter to your application you should either avoid using it when
a leap second is inserted or find out exactly how your system does things and
design the application appropriately.





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