On 2011-01-28 18:34, Gerard Ashton asked:
Windows and Unix have general reputations of not doing it right; does anyone know of a hardware/operating system combination that handles leap seconds correctly? If so, does it have a defined approach to providing a quasi-UTC that hides leap seconds to applications that wish to live in blissful ignorance?
No, I do not know where it is done "correctly" -- I just know some programming languages where datetimes and time scales are modelled in other ways than in the JSR-310 proposal. Let me just mention two. Take ADA95, for example. The language accepts the existence of various independent time scales, that is, physical quantities that all take their values in the same space of datetimes. That space provides the operations of an affine space over the one-dimensional vector space of times, with units s, min, h, d, etc. Datetimes values can be denoted using calendars or with affine units such as Julian dates or Besselina epochs. Whether values of one time scale can be converted (in whatever sense) to values of another time scale is not imposed by the interface. Some time scales can be converted exactly (eg, TCG to TT), some exactly only for past epochs (eg, UTC and TAI), some only approximately, even for the past (eg, TT to TAI). ADA95 also recognizes the fact that it is sometimes needed to add additional information to a datetime value: viz, the information that the datetime value occurs twice in a non-monotone time scale. This is needed to order such amended datetime values in the case of leap seconds, and in the case of civil time scales while they switch from summer time to winter time. Other additional operations on these values comprise better conversions to other time scales, eg, unambiguous conversion from UTC to TAI, or from civil time to UTC with the help of a zic file. SQL provides datetime values with an additional offset so that they comprise both a local time scale and a UTC value. This is another form of amended datetime values that is important in applications. It can also model a UTC time stamp with known offset to TAI. This amendment is independent of the previous one, so that I would expect a complete support to provide datetime types with both amendments, too. I have left out all the gory details and I hope this comment is still not too abstract. Michael Deckers. _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
