update leap second table to 28 Jun 2025 based on IERS Bulletin C 68

[AndreHauschild]

According to IERS Bulletin C 68 no leap second will be introduced at the end of December 2024. The next possible insertion date is therefore end of June 2025.

[scottstanie]

Thanks for noting this- do we have no way to check in the code that the time period is valid? That seems like a useful check to run in python before calling the Fortran module

[AndreHauschild]

That is a good question! My understanding is that for performance reasons, solid.for has a hard-coded implementation of this file with the leap second history from IERS, which is subsequently updated based on the most recent Bulletin C. This file also contains a validity end date, after which the next leap second could be inserted. From what I see in the commit history, this date has periodically been updated in the source code.

The only option I can think of as an altenative to this manual procedure is to retrieve the most recent version of the leap second history from the IERS website at run-time and then check the date. But I do not think that is a practical approach.

[rtburns-jpl]

I know that in C, there is typically a leapsecond file as part of the libc (e.g. https://github.com/bminor/glibc/blob/master/timezone/leapseconds) so any code using libc for UTC conversions will continue to work without recompilation as long as libc is kept up to date. Does anything similar exist for fortran?

[yunjunz]

LGTM. Thank you @AndreHauschild.