From
http://forum.world.st/What-s-up-on-build-squeak-org-tp4760266p4760319.html :
David T. Lewis wrote
> I have been working on a variation of class DateAndTime that replaces its
> instance variables (seconds offset jdn nanos) with two instance variables,
> utcMicroseconds to represent microseconds elapsed since the Posix epoch,
> and
> localOffsetSeconds to represent the local time zone offset. When
> instantiating
> the time now, A single call primitiveUtcWithOffset is used to obtain these
> two values atomically as reported by the underlying platform.
>
> There are several advantages to this representation of DateAndTime, the
> most
> important of which is that its magnitude is unambiguous regardless of
> daylight
> savings transitions in local time zones.
>
> This is my attempt to address some historical baggage in Squeak. The VM
> reports time related to the local time zone, and the image attempts to
> convert to UTC (sometimes incorrectly). A UTC based representation makes
> the
> implementation of time zone tables more straightforward (see for example
> the Olson time zone tables in TimeZoneDatabase on SqueakMap).
>
> I am attaching the source code as a SAR file that can be loaded into a
> fully
> updated Squeak trunk image. The conversion process is slow, so be patient
> if you load it.
>
> This can be run on either an intepreter VM or Cog, but if you use Cog,
> please
> use a version dated June 2013 or later (the VM in the Squeak 4.5
> all-in-one
> is fine).
>
> I am also attaching a copy of LXTestDateAndTimePerformance, which can be
> used to compare the performance of some basic DateAndTime functions.
>
> Performance of the UTC based DateAndTime is generally favorable compared
> to
> the original. Here is what I see on my system (smaller numbers are
> better).
>
> LXTestDateAndTimePerformance test results using the original Squeak
> DateAndTime
> on an interpreter VM:
> {
> #testNow->10143 .
> #testEquals->30986 .
> #testGreaterThan->80199 .
> #testLessThan->75912 .
> #testPrintString->10429 .
> #testStringAsDateAndTime->44657
> }
>
> LXTestDateAndTimePerformance test results using the new UTC based
> DateAndTime
> on an interpreter VM:
> {
> #testNow->6423 .
> #testEquals->31625 .
> #testGreaterThan->22999 .
> #testLessThan->18514 .
> #testPrintString->12502 .
> #testStringAsDateAndTime->32912
> }
>
> (CC to Brent Pinkney, author of the excellent Squeak Chronology package)
>
> Dave
>
>
>
>
>
> UtcDateAndTime-dtl.sar (40K)
> <http://forum.world.st/attachment/4760319/0/UtcDateAndTime-dtl.sar>
> LXTestDateAndTimePerformance.st (2K)
> <http://forum.world.st/attachment/4760319/1/LXTestDateAndTimePerformance.st>
-----
Cheers,
Sean
--
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