Chris Muller uploaded a new version of Kernel to project The Trunk:
http://source.squeak.org/trunk/Kernel-cmm.607.mcz

==================== Summary ====================

Name: Kernel-cmm.607
Author: cmm
Time: 17 July 2011, 3:19:27.832 pm
UUID: 707fff1e-e5d5-46e9-9c87-75010916820b
Ancestors: Kernel-nice.605

- Size and speed optimization for DateAndTime, Date, and other Timespans.  By sending them the new #makeUTC message, Dates can now share a canonicalized #zero 'offset' Duration.  Hashing Dates created in offset zero is many times faster than those with other offsets.
- Since there are typically many Dates in the system, their 1-day 'duration' is also shared.

=============== Diff against Kernel-nice.605 ===============

Item was changed:
  SharedPool subclass: #ChronologyConstants
  	instanceVariableNames: 'seconds offset jdn nanos'
+ 	classVariableNames: 'DayNames DaysInMonth MonthNames NanosInMillisecond NanosInSecond OneDay SecondsInDay SecondsInHour SecondsInMinute SqueakEpoch Zero'
- 	classVariableNames: 'DayNames DaysInMonth MonthNames NanosInMillisecond NanosInSecond SecondsInDay SecondsInHour SecondsInMinute SqueakEpoch'
  	poolDictionaries: ''
  	category: 'Kernel-Chronology'!
  
  !ChronologyConstants commentStamp: 'brp 3/12/2004 14:34' prior: 0!
  ChronologyConstants is a SharedPool for the constants used by the Kernel-Chronology classes.!

Item was changed:
  ----- Method: Date class>>starting: (in category 'squeak protocol') -----
+ starting: aDateAndTime 
+ 	^ super
+ 		starting: aDateAndTime midnight
+ 		duration: Duration oneDay!
- starting: aDateAndTime
- 
- 	^super starting: (aDateAndTime midnight) duration: (Duration days: 1)!

Item was added:
+ ----- Method: DateAndTime>>makeUTC (in category 'squeak protocol') -----
+ makeUTC
+ 	"Change the receiver's timezone to UTC. Like #asUTC, but modifies the receiver and is much faster."
+ 	self primOffset: Duration zero!

Item was added:
+ ----- Method: DateAndTime>>primOffset: (in category 'private') -----
+ primOffset: aDuration
+ 	offset := aDuration!

Item was added:
+ ----- Method: Duration class>>initialize (in category 'initialize-release') -----
+ initialize
+ 	ChronologyConstants classPool
+ 		at: #Zero
+ 		put:
+ 			(self basicNew
+ 				seconds: 0
+ 				nanoSeconds: 0) ;
+ 		at: #OneDay
+ 		put: 1 day!

Item was added:
+ ----- Method: Duration class>>oneDay (in category 'squeak protocol') -----
+ oneDay
+ 	"Answer the canonicalized Duration representing length of 1 day.  Used by Dates."
+ 	^ OneDay!

Item was changed:
  ----- Method: Duration class>>zero (in category 'ansi protocol') -----
  zero
+ 	"Answer the canonicalized instance of Duration zero."
+ 	^ Zero!
- 
- 	^ self basicNew seconds: 0 nanoSeconds: 0
- !

Item was added:
+ ----- Method: Timespan>>makeUTC (in category 'squeak protocol') -----
+ makeUTC
+ 	"Change the receiver's timezone to UTC, which affords substantially better hashing performance."
+ 	start makeUTC!