Thomas Koenig tomkoenig at mindspring.com
Mon May 8 23:25:32 UTC 2006

John, Wow. Thanks for your quick and clear response.  Three things. 1. I
will submit the FIX to remove the original assertion since it's not longer
valid.  2.  I'll park the incomplete test issue as a Mantis BUG item unless
you already have and until someone provides the release number.  3.  I'll
defer to more skilled randomologists on the issue of repeating seeds.

> -----Original Message-----
> From: squeak-dev-bounces at lists.squeakfoundation.org [mailto:squeak-dev-
> bounces at lists.squeakfoundation.org] On Behalf Of John M McIntosh
> Sent: Sunday, May 07, 2006 3:05 PM
> To: The general-purpose Squeak developers list
> Subject: Re: UUIDPrimitivesTest>>testCreationRandom
> Well first some background
> See
> http://www.webdav.org/specs/draft-leach-uuids-guids-01.txt
> Most  current Squeak VMs provide a primitive that asks the operating
> system to generate a UUID, I believe that is true for unix,
> macintosh, and windows now. If such a primitive does not exist we
> generate a UUID using the UUID version 4, which it is a randomly or
> pseudo-randomly generated 60 bit value generated by Smalltalk code.
> Those 60 bits of random data come from looking at the results of
> Random which is is an adaptation of the Park-Miller RNG.
> See UUIDGenerator>>generateOneOrZero
> In this routine we reset the generator to a random starting point on
> unix based or macintosh machines using /usr/urandom, or by using a
> formula based on the millisecond clock every 100,000 iterations. Mmm
> in looking at that I wonder what the probability of getting a seed is
> that is a repeat of a previously used seed.
> Perhaps that if clause should be removed? Thoughts?
> I'll note the first bug discovered here was that we reset the Random
> number to a static value at image startup time, that caused the UUID
> generation using UUIDGenerator to repeat on image startups that did
> not involve saves, hence a startup method was added to reset the
> generator at image startup time.
> But back to the question.
> You see originally the type of UUID generated by the operating system
> would have the last twelve bytes the same since that was the bits
> from the ethernet interface card. The testCreationRandom checks to
> see if those bytes are the same, if not then it assumes the UUID is a
> randomly generated UUID and then does a simple pass to see if there
> are any duplicates in a short sequence and checks flags to see if
> this is a random UUID, that as you noticed fails.
> So why.
> Ah, well because someone noticed that if you were tagging things with
> UUIDs, a thing that I believe Microsoft office does? Then why it's
> possible to determine which Windows computer generated that UUID, or
> at least which ethernet card was in use at the time of editing. Since
> that was a privacy concern Microsoft changed the algorithm to one-way
> (right, I"m sure) hash the entire UUID.
> Therefore the testCreationRandom test likely should be deleted unless
> we are using the UUIDGenerator because the UUID has been hashed and
> none of the should:[] are valid.
> Lastly
> See earlier notes on this subject
> http://lists.squeakfoundation.org/pipermail/squeak-dev/2003-January/
> 051248.html
> I'll note the test
> 	Smalltalk platformName asLowercase = 'win32' ifTrue:
> 		["Some microsoft platforms one-way hash the UUID so this
> gets
> invoked
> 		however it will fail because the UUID could be node-based,
> only
> solution is to
> 		terminate the test early"
> 		^self].
> is now not complete, since in current versions of OS-X apple also
> decided to hash the uuid values they generate.
> I'm not sure at what version of os-x they started doing this.
> Therefore someone would need to add a test to see if platform is
> SmalltalkImage current platformName asLowercase = 'mac os'
> and
> consider
> SmalltalkImage current osVersion asNumber < ????
> to check os-x at a paricular version cutoff point.
> On 7-May-06, at 10:54 AM, Thomas Koenig wrote:
> > John M McIntosh,
> > Hi, I think you created UUID and its test case UUIDPrimitivesTest?
> > Do you
> > have time to help resolve the problem?
> >
> > UUIDPrimitivesTest>>testCreationRandom fails on this assertion
> >  self should: [((UUID new at: 7) bitAnd: 16rF0) = 16r40].
> > Here's what I can tell you:
> > -The failure occurs in 3.9b 7029 and in 3.8 6665
> > -I'm testing on win xp
> > -the assertion appears to fail the very first time (it's in a
> > repeats 1000)
> > -(self at: 7) bitAnd: 16rF0 ==> 32 (not 64)
> > -the other assertion passes always.
> >
> > Thanks
> > Tom
> >
> >
> >
> --
> ========================================================================
> ===
> John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
> Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
> ========================================================================
> ===

More information about the Squeak-dev mailing list