Re: A lurker surfaces

2006-12-30 Thread Rob Seaman

Jim Palfreyman wrote:


With my time hat on, having time that is discontinuous pains me. It
doesn't make sense in my heart. But at least these
discontinuities are in whole seconds.

Any discontinuities must be regularly done. So they are part of all
computer systems and are tested and used all the time. Don't let
them build for a decade - that is bad bad news.


Just a reminder that UTC has no - none - nada - discontinuities.
Various computer mis-implementations may, but the standard is very
carefully constructed to avoid spring-forward or fall-back gaps or do-
overs.

This is just one of many flaws of the notion of leap hours.  A leap
hour (like a leap second or leap day) is an extra intercalary
temporal unit inserted into the continuous flow of time.  A leap hour
is NOT an unmatched fall back do-over - the day in question would
have 25 regular, ordinary, permanent, unique hours - and the extra
hour would occur contemporaneously worldwide.  It would not involve
an easy floating 2 am Sunday local clock reset.

So, for example, if the leap hour is 2606-12-31, 24:00:00 to 24:59:59
UT, it would fall BETWEEN 18:59:59 and 19:00:00 EST, just like a leap
second today is 23:59:60 UT or 18:59:60 EST, also falling between
18:59:59 and 19:00:00.  In each time zone in turn, the leap hour
would fall between different otherwise sequential clock ticks - a non-
issue with a leap second, not so easy to ignore with a leap hour.
Still not a discontinuity, but certainly a real pain for anyone who
is trying to keep the events of the day straight.

More than likely, the hour would be labeled the same worldwide, so
the EST clock would run 18:59:58, 18:59:59, 24:00:00, 24:00:01, ...,
24:59:58, 24:59:59, 19:00:00, 19:00:01, ...

Rob


Re: A lurker surfaces

2006-12-30 Thread M. Warner Losh
In message: [EMAIL PROTECTED]
Rob Seaman [EMAIL PROTECTED] writes:
: Just a reminder that UTC has no - none - nada - discontinuities.

At the very least, the TAI-UTC difference is discontinuous with jumps
at the leap seconds.  One could easily suggest that 'UTC has
discontinuities' really is a shorthand way of saying this.  One could
also call them irregularities, like the time scale is constipated, as
well.

And the variable radix seems to be to be a crude way to define away
the problem.  You never know, unless you look it up in a table, when
to do the variation in the radix.

: Various computer mis-implementations may, but the standard is very
: carefully constructed to avoid spring-forward or fall-back gaps or do-
: overs.

Well, if you count the variable radix notation as being 'continuous'
then maybe you are right.  However, you never know when the radix is
variable, hence the assertion on many people's part that UTC is
discontinuous.

Warner