[Vm-dev] Status of LargeIntegersPlugin

David T. Lewis lewis at mail.msen.com
Wed Jul 23 03:20:18 UTC 2014

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?


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