[pypy-dev] Re: [ann] Minimal Python project
pedronis at bluewin.ch
Thu Jan 16 13:57:02 CET 2003
From: "Christian Tismer" <tismer at tismer.com>
> > Will you give some thought to going to a tagged representation of
> > object references, and maybe a more traditional GC? That way you
> > avoid a lot of memory traffic, and also don't have to adjust reference
> > counts every time you touch anything.
> > I think these would give a big performance boost, and also would also
> > simplify the C API. It might be possible to supply a compatibility
> > layer to make the old C API still useable.
> Can you give me a hint how this would be done?
> I have no experience with tagged representations,
> but if this can save so much, I should learn more
> about it.
this is a relevant survey paper:
Representing Type Information in Dynamically Typed Languages
integer in the range [-2**30,2**30-1] would be represented by their bit
patterns shifted left by 1 bit
all other objects would be boxed, and the address left shifted by 1 and ORed
The fact that Python is slowly removing the long/integer separation can make
less disruptive such an approach.
OTOH I think such an approach would make the life a bit more complicated for
psyco when detecting that a datum has machine-size integer type, because such a
datum would be either in the first form _or_ a boxed (long) integer in the
larger range -2**31 2**31-1.
Another approach is to carry data around as a struct where both the tag and the
datum are machine words, this approach is AFAIK currently used in the Gwydion
Dylan compiler (www.gwydiondylan.org) originally developed at CMU.
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