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

[Nicolas Cellier]

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

Nicolas
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