[Vm-dev] VM Maker: VMMaker.oscog-eem.790.mcz

[David T. Lewis]

On Wed, Jul 02, 2014 at 07:44:26AM +0200, Nicolas Cellier wrote:
>  
> 2014-07-02 0:28 GMT+02:00 David T. Lewis <lewis at mail.msen.com>:
> 
> >
> > On Tue, Jul 01, 2014 at 09:21:00PM +0200, Nicolas Cellier wrote:
> > >
> > > 2014-07-01 4:22 GMT+02:00 <commits at source.squeak.org>:
> > >
> > > >
> > > > Item was changed:
> > > >   ----- Method: LargeIntegersPlugin>>cDigitSub:len:with:len:into: (in
> > > > category 'C core') -----
> > > > + cDigitSub: pByteSmall len: smallLen with: pByteLarge len: largeLen
> > into:
> > > > pByteRes
> > > > +       | z |
> > > > - cDigitSub: pByteSmall
> > > > -               len: smallLen
> > > > -               with: pByteLarge
> > > > -               len: largeLen
> > > > -               into: pByteRes
> > > > -       | z limit |
> > > >         <var: #pByteSmall type: 'unsigned char * '>
> > > >         <var: #pByteLarge type: 'unsigned char * '>
> > > >         <var: #pByteRes type: 'unsigned char * '>
> > > >
> > > > +       z := 0. "Loop invariant is -1<=z<=1"
> > > > +       0 to: smallLen - 1 do:
> > > > -       z := 0.
> > > > -       "Loop invariant is -1<=z<=1"
> > > > -       limit := smallLen - 1.
> > > > -       0 to: limit do:
> > > >                 [:i |
> > > >                 z := z + (pByteLarge at: i) - (pByteSmall at: i).
> > > > +               pByteRes at: i put: z - (z // 256 * 256).
> > "sign-tolerant
> > > > form of (z bitAnd: 255)"
> > > >
> > >
> > > Frankly, having z declared unsigned int and just doing  pByteRes at: i
> > put:
> > > (z bitAnd: 16rFF) as I suggested would be way way simpler and will ALWAYS
> > > work.
> > > Why the hell invoke the complications of signed arithmetic when the
> > content
> > > pByteRes is unsigned???
> >
> > Nicolas,
> >
> > This sounds right to me.
> >
> > Do you have a final version of #cDigitSub:len:with:len:into: that you can
> > recommend? The version in VMMaker-nice.342 produces failures in the
> > KernelTests-Numbers tests when compiled in 64-bit mode, but I think that
> > you have since suggested some other improvements in this email thread.
> >
> > Dave
> >
> >
> Hi David,
> that's interesting. VMMaker-nice.342 contains all the 32bits LargeInteger
> modifications, not just the #cDigitSub:len:with:len:into:.
> I tried to declare everything as <unsigned int> rather than <usqInt> with
> the assumption that sizeof(unsigned int)*2==sizeof(unsigned long long).
> But I never tried to compile a 64 bits VM, I think I lost the recipe for
> brewing such a flavour.
> I'm on MacOSX, could you provide a link to the shortest way to do it?
> Once I can check it, I'll publish a corrected version.
> Thanks

Hi Nicolas,

Starting with an up to date VMMaker (trunk), I loaded #cDigitSub:len:with:len:into:
from VMMaker-nice.342, then compiled the VM on 64-bit Linux and ran the unit tests.

I also ran tests on the 64-bit image with 64-bit VM, and this did *not* show
any problem.

Sorry I did not look into it further, I will try to do so as soon as I get
some time.

Dave