[Vm-dev] Status of LargeIntegersPlugin

[David T. Lewis]

On Wed, Jul 23, 2014 at 11:44:42AM +0200, Nicolas Cellier wrote:
>  
> 2014-07-23 5:20 GMT+02:00 David T. Lewis <lewis at mail.msen.com>:
> >
> > Moving discussion back to vm-dev, as it may be of some general interest.
> >
> > On Tue, Jul 22, 2014 at 09:16:23AM -0700, Eliot Miranda wrote:
> > > On Mon, Jul 21, 2014 at 5:35 PM, David T. Lewis <lewis at mail.msen.com>
> > wrote:
> > >
> > > > Hi Eliot,
> > > >
> > > > I want to check before I copy this update to the VMMaker repository -
> > are
> > > > you in agreement with using Nicolas' LargeIntegerPlugin? It seems fine
> > to
> > > > me, so I'll move it to VMM trunk if you agree.
> > > >
> > >
> > > Well, it is goodness.  My concern is that it requires image changes to
> > make
> > > image code still function, but haven't had time to check it out.  The
> > issue
> > > is that currently, large integers are in little endian order and code in
> > > the image accesses bytes in large integers assuming that the bytes
> > there-in
> > > are in little endian order.  For example see digitCompare: and digitAt:.
> > >  Now digitAt: is implemented as simply primitive 60, the standard at:
> > > primitive.  So on current VMs a big-endian large integer will /not/ be
> > > correctly accessed via digitAt:.
> > >
> > > Am I right?
> >
> > I do not have a big endian machine to check this, but my assumption is that
> > since Squeak began on big endian machines and moved to little endian
> > later, and since the LargeIntegersPlugin has been around for a long time,
> > and since images migrated across big and little endian platforms without
> > any apparent problem, then we probably do not have any endianness problems
> > with the existing plugin.
> >
> > I wrote a few tests (and added them to trunk) to validate the digit access
> > methods. These tests pass on my little endian PC with a Cog VM using the
> > old plugin, and they also pass with Nicolas' new LargeIntegersPlugin with
> > both the 32-bit and 64-bit image formats.
> >
> > Nicolas' updated plugin seems to be fully compatible with the original
> > LargeIntegersPlugin, and it produces the expected results for all of the
> > image formats and VMs that I am able to test. I cannot confirm this for
> > a big endian platform, but I think that any errors on  big endian box
> > would be exposed by the unit tests.
> >
> > It looks good to me.
> >
> > Nicolas, any concerns or comments?
> >
> > Thanks,
> > Dave
> >
> >
> There are two versions of my work
> - one using 32 bits digits which is my original work commented on my blog
> http://smallissimo.blogspot.fr/2012/12/accelerating-largeinteger-in-squeak.html
> and following posts that you can find on MC repository
> http://smalltalkhub.com/mc/nice/NiceVMExperiments/main
> - a backport of this work for 8 bit digits that I failed to commit due to
> zip bug, and that I sent as a change set
> I didn't check, but presumably you integrated the last one for 8 bit digits.
> So there should be no problem of endianness

Nicolas,

Yes, I integrated the second one for 8 bit digits. I will go ahead and move it
into the VMMaker repository, and commit the ./src files for trunk SVN.

Thank you!

Dave