[Vm-dev] VM Maker: VMMaker-dtl.350.mcz

[Eliot Miranda]

Hi David,

On Mon, Sep 8, 2014 at 12:18 PM, David T. Lewis <lewis at mail.msen.com> wrote:

>
> I know that "unsigned" means "unsigned int". That is the intent.
>
> With the primitive as currently implemented, that variable must be 32
> bits, otherwise the shift left can successfully produce a five byte large
> integer that is truncated to four without failing the primitive. This
> change is to fix the current implementation of the primitive in the case
> of sizeof(sqInt) == 8.
>

OK, then it is fixing it in a way that will break a 64-bit implementation
that uses 64-bit SmallIntegers.   Personally I find the method defective
(for reasons already stated), and will be rewriting it soon.


> Dave
>
> >  Hi David,
> >
> >    and another issue is that "unsigned" is shorthand for "unsigned int",
> > so
> > if you wanted to generalize the method to handle integers of the system's
> > word size (as is the case with 64-bit Spur which will have 61-bit
> > SmallIntegers, unlike the 31-bit SmallIntegers in 64-bit Squeak) you'd
> > want
> > to use "usqInt", not "unsigned".
> >
> > On Sat, Sep 6, 2014 at 8:45 PM, <commits at source.squeak.org> wrote:
> >
> >>
> >> David T. Lewis uploaded a new version of VMMaker to project VM Maker:
> >> http://source.squeak.org/VMMaker/VMMaker-dtl.350.mcz
> >>
> >> ==================== Summary ====================
> >>
> >> Name: VMMaker-dtl.350
> >> Author: dtl
> >> Time: 6 September 2014, 11:44:28.389 pm
> >> UUID: 2ad132b0-5fb3-4580-b5a8-29af12c3cb81
> >> Ancestors: VMMaker-dtl.349
> >>
> >> VMMaker 4.13.6
> >>
> >> Fix primitiveBitShift (primitive 17) for sqInt declared 64 bits, as in a
> >> VM for 64-bit image format 68002.
> >>
> >> In image format 68002, bit shift left failed because of return type
> >> limited to a 32-bit large integer, but internally the primitive
> >> successfully shifted left into a variable declared as a 64 bit sqInt..
> >> The
> >> simple fix (implemented here) is to declare the variable as 32 bit
> >> unsigned
> >> to agree with the 32-bit logic of the existing primitive.
> >>
> >> Note that permitting a left shift into a 64 bit variable makes sense
> >> generally, and the primitive could be recoded to accomodate this for
> >> shift
> >> left, with the primitive answering positive64BitIntegerFor: rather than
> >> positive32BitIntegerFor: in the case of a shift left to allow for the
> >> greater range (not implemented in this update).
> >>
> >> With this update, all KernelTests-Numbers tests pass for the 64-bit
> >> image
> >> format 68002.
> >>
> >> =============== Diff against VMMaker-dtl.349 ===============
> >>
> >> Item was changed:
> >>   ----- Method: InterpreterPrimitives>>primitiveBitShift (in category
> >> 'arithmetic integer primitives') -----
> >>   primitiveBitShift
> >>         | integerReceiver integerArgument shifted |
> >> +       <var: #shifted type: 'unsigned'>
> >> +
> >>         integerArgument := self popInteger.
> >>         integerReceiver := self popPos32BitInteger.
> >>         self successful ifTrue: [
> >>                 integerArgument >= 0 ifTrue: [
> >>                         "Left shift -- must fail if we lose bits beyond
> >> 32"
> >>                         self success: integerArgument <= 31.
> >>                         shifted := integerReceiver << integerArgument.
> >>                         self success: (shifted >> integerArgument) =
> >> integerReceiver.
> >>                 ] ifFalse: [
> >>                         "Right shift -- OK to lose bits"
> >>                         self success: integerArgument >= -31.
> >>                         shifted := integerReceiver >> (0 -
> >> integerArgument).
> >>                 ].
> >>         ].
> >>         self successful
> >>                 ifTrue: [self push: (self positive32BitIntegerFor:
> >> shifted)]
> >>                 ifFalse: [self unPop: 2]!
> >>
> >> Item was changed:
> >>   ----- Method: VMMaker class>>versionString (in category 'version
> >> testing') -----
> >>   versionString
> >>
> >>         "VMMaker versionString"
> >>
> >> +       ^'4.13.6'!
> >> -       ^'4.13.7'!
> >>
> >>
> >
> >
> > --
> > best,
> > Eliot
> >
>
>
>


-- 
best,
Eliot
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