[Vm-dev] primitiveBitShift

[Igor Stasenko]

On 15 April 2013 11:31, Helmut Rohregger <helmut.rohregger at gmail.com> wrote:
>
> Hi all,
>
> i am interested in the implementations of primitives in the VMMaker package
> and found some code, which i think may be implemented incorrectly.
> Maybe some of you can help me out and correct me if i am wrong.
>
> Its located in InterpreterPrimitives>>#primitiveBitShift (VMMaker-dtl.319):
> the code: "self success: integerArgument <= 31" checks, if we lose bits by
> shifting to the left. This is because of processing SmallIntegers here,
> isn't it? But a "1 bitShift: 31" will produce a LargePositiveInteger instead
> of a SmallInteger. In fact a left shift of 30 will produce a
> LargePositiveInteger too.
>
> I know the code works, because the resulting object gets checked being a
> SmallInteger and fails if not. But the correct check would be "self success:
> integerArgument <= 29", isn't it?
> What do you think?
>

hmm., how do you know if shifted result will fit into smallint, if you
don't check both operands?

"1 << 29 " fits
"SmallInteger maxVal << 29 " doesnt.
even
"SmallInteger maxVal << 1 " doesnt.

> - helmut
>
>



-- 
Best regards,
Igor Stasenko.