bugGNU Octave - Bugs: bug #53910, Documentation of Leap Seconds

 
 

bug #53910: Documentation of Leap Seconds

Submitter:  Ian McCallion <ianmcc>
Submitted:  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:  Open/Closed:  * Open
Release:  * 4.4.0 Operating System:  * Any
Fixed Release:  None Planned Release:  None
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Tue 15 May 2018 01:57:06 PM UTC, original submission:  

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.


Ian McCallion <ianmcc>

 

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