[Vm-dev] About primitiveBitAnd / Or / Xor

[Eliot Miranda]

On Tue, Mar 17, 2015 at 2:38 PM, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:

>
>
> Hi again,
> I've noticed the COG code currently branches on objectMemory wordSize = 8
> condition,
> to either load self positive64BitValueOf: integerArgument.
> or to load self positive32BitValueOf: integerArgument.
>
> Of course, this could be resolved to a single
>     integerArgument := self positiveMachineIntegerValueOf: integerArgument
> which will care of the branch by itself...
> That's what I did.
>
> But maybe the intention was rather to deal with signed64BitValueOf in the
> 64 bit branch like what was done to primitiveBitShift?
>

Right.  I want to avoid the call altogether in that case.


Of course, all this is assuming that the machine uses a 2-complement
> implementation, otherwise it won't match the Smalltalk semantic.
> That's not so rare ;) - but theoretically not fully portable - contrarily
> to actual strategy which is fully portable.
> Since other parts of the VM also rely on such specific, maybe we can trade
> a little portability tribute for the sake of speed.
>

Yes, for me trying to make the VM portable to non-2's compliment systems
isn't worth it.  I remember that there's a fair bit of code in HPS that
tries to cope with systems that don't have 8-bit bytes.  Again pointless.
The world is more homogenous now than it was in the time of PDP-10s, and
that's a good thing.  If some feature isn't exercised it atrophies and
becomes a hindrance.



>
> Thoughts?
>

> Nicolas
>
>


-- 
best,
Eliot
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