I would like to consider offering UTCDateAndTime for inclusion in trunk.

On 64-bit Spur, overall performance is almost twice that of the base Chronology
package. In addition, the representation of DateAndTime as Posix time plus time
zone offset is simpler and easier to test and understand.

I cannot easily put this into the inbox, but loading the package into a trunk
image is done as follows:

      (MCMcmUpdater
      	updateMapNamed: 'update'
      	repository: 'http://www.squeaksource.com/UTCDateAndTime')
      	doUpdate: false.

I have not modified any of the Chronology tests. After loading UTCDateAndTime
into a trunk image, here are the tests that will fail, along with my explanation
for the failures:

  DateAndTimeEpochTest>>testHash
      - DateAndTime>>hash works differently now. Test should be either
        updated or eliminated.

  DateAndTimeLeapTest>>testAsSeconds
      - Discussion required. I claim that #asSeconds can only make sense
        if it means elapsed seconds since the epoch. The prior implemention
        and the test are both wrong.

   DateAndTimeLeapTest>>testHash
      - DateAndTime>>hash works differently now. Test should be either
        updated or eliminated.

   DateAndTimeTest>>testPrecision
      - Discussion required. It is simply wrong to assume that two calls
        to DateAndTime class>>now will always answer different values, and
        it is even more wrong to fudge the clock accessors to make it appear
        to be doing this when it is not. Yes I know that certain database
        applications require distinct time stamps, but hacking the actual
        system clock is not the right thing to do.

  TimespanDoTest>>testDatesDo
      - Need to change the test setUp method. The original intent is to test
        date iteration using a time span begining with a UTC midnight. Test
        will pass if the start time is constructed accordingly. Note however
        that date iteration is suspect for durations starting at times other
        than midnight in the local time zone, so additional tests may be needed.

  TimespanDoTest>>testNext
      - Same issue as testDatesDo, fix the setUp method and the test will pass,
        but additional tests may be needed.


The necessary #primitiveUtcWithOffset is present in all Cog/Spur/interpreter VMs.
It is an optional named primitive (not numbered). If not present, the fallback
code uses the Posix epoch for all new time values, resulting in a runnable image
but with incorrect time stamps for new DateAndTime instances. Falling back to the
original millisecond clock logic and primitives is possible, but it seemed to me
to be an unnecessary complication so I got rid of it.

Does anyone think that adding UTCDateAndTime to trunk is /not/ a good thing to do?

Dave