RE: How do tagged data structures work in Strongtalk?

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of prunedtree
> Sent: Monday, May 28, 2007 3:14 AM
> To: Strongtalk-general
> Subject: Re: How do tagged data structures work in Strongtalk?
>
>
>
> On May 27, 10:38 pm, nicolas cellier <[email protected]> wrote:
> > What about something like VW SmallDouble on a 64 bits machine?
> > (two tag bits taken from exponent i think)
>
> Tagged doubles have the same advantage than unboxed doubles: They
> bypass allocation. Their advantage is that they don't break the object
> model. But strongtalk works only for x86-32 and will stay like that
> for quite some time.
>
> Btw, I think we should get rid of the unboxed doubles in smalltalk
> code. Sure, they currently show us the cost of allocation for 64bit fp
> computation, and they are useful for that, but the strongtalk compiler
> is made to overcome this in the long term. For instance, with some
> escape analysis it would be easy to enable object recycling in
> compiled code, and thus remove most of the allocated doubles in
> computations. Life analysis can easily infer that for many doubles we
> allocate, old ones die, and thus you can reuse them (eg: z_im := two *
> z_re * z_im + c_im). Conceputally, it's like changing +/-/* operators
> into +=/-=/*=. It doesn't change semantics because the objects we
> recycle are garanteed to be garbage.
>
> It makes little sense to keep unboxed doubles in a smalltalk system
> like strongtalk, whose emphasis is achieving good performance on
> idiomatic smalltalk code. You will find under the "computation"
> category of the Mandelbrot class several exemples of the general code
> I would like to avoid.

Yes, I agree that the unboxed doubles in Strongtalk right now do not fit
with the language model.  They were not planned part of the project in the
first place; they were simply an experiment that Robert Griesemer did on his
own because he felt it was easy to do- we discussed this at the time, but
clearly a general model that matches Smalltalk semantics is a lot more work,
and isn't going to happen anytime soon.

And anyway, many things are higher priority than this right now.

Cheers,
Dave


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