Thomas Bushnell, BSG scripsit: > Posix should never have done what they did. But they did it, and now there > is a serious problem if Scheme diverges.
Well, here's what Wikipedia says about what happened in the committee: [T]he Unix time scale was originally intended to be a simple linear representation of time elapsed since an epoch. However, there was no consideration of the details of time scales, and it was implicitly assumed that there was a simple linear time scale already available and agreed upon. Indeed, the first edition manual's definition doesn't even specify which timezone is used. Several later problems, including the complexity of the present definition, result from Unix time having been defined gradually by usage rather than fully defined to start with. When POSIX.1 was written (it was published in 1988), the question arose of how to precisely define time_t in the face of leap seconds. Some argued for it to remain, as intended, a linear count of seconds since the epoch, at the expense of complexity in conversions with civil time. Others argued for it to remain, as conflictingly intended, easily interconvertible with the conventional representation of civil time, at the expense of inconsistency around leap seconds. Computer clocks of the era were not sufficiently precisely set to form a precedent one way or the other. The POSIX committee was swayed by arguments against complexity in the library functions, and firmly defined the Unix time in a simple manner in terms of the elements of UTC time. Unfortunately, this definition was so simple that it didn't even encompass the entire leap year rule of the Gregorian calendar, and would make 2100 a leap year. The 2001 edition of POSIX.1 rectified the faulty leap year rule in the definition of Unix time, but retained the essential definition of Unix time as an encoding of UTC rather than a linear time scale. Also, since the mid-1990s computer clocks have been routinely set with sufficient precision for this to matter, and they have most commonly been set using the UTC-based definition of Unix time. This has resulted in considerable complexity in Unix implementations, and in the Network Time Protocol, to execute steps in the Unix time number whenever leap seconds occur. -- I could dance with you till the cows John Cowan come home. On second thought, I'd http://www.ccil.org/~cowan rather dance with the cows when you [email protected] come home. --Rufus T. Firefly _______________________________________________ Scheme-reports mailing list [email protected] http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports
