Hi Ian,

> You might also find the following useful:
>
>   http://www-sor.inria.fr/~piumarta/esug98/slides.ps.gz
>
> starting around page 33.

    Indeed, the whole document is very useful and interesting to read.

    Thanks a lot, Ian.

    BTW, were you teasing ?

    On page 17 you mentioned a 'violently stripped' thingy. ;-)

    Where can I find such a beauty ?

    Of course, I would love to lay my hand on an 'eXtremely violently
stripped' one.

    The smaller the more fun. Size does matter ;-)

    Again, many thanks for the explanation and the document.

    Cheers,

    PhiHo.

    P.S: Now I also understand what it means by Blue Plane and Pink Plane.
    Just wondering what colorful plane is Squeak now riding.
    (Are Grey or Black also considered colors ? )


----- Original Message -----
From: "Ian Piumarta" <ian.piumarta at inria.fr>
To: <phiho.hoang at rogers.com>
Cc: <squeak-dev at lists.squeakfoundation.org>
Sent: Sunday, October 13, 2002 4:47 PM
Subject: Re: Object Format


> On Sun, 13 Oct 2002, PhiHo Hoang wrote:
> > - 4 bits object format
> >
> > What is this 4-bit 'object format' field.
>
> It tells you about what the instance contains.
>
> The top bit (bit 3) is 1 for byte objects, 0 for word/pointer objects.
>
> If the top bit is zero (words/pointers) then:
> Bit 2 is 0 for pointer objects, 1 for words.
> Bit 1 is set if there are indexable fields, 0 if there are none.
> Bit 0 is set if there are fixed fields (named inst vars), otherwise 0.
>
> A "word" object (bit 2 set) that has neither indexable nor fixed fields
> (bits 1 and 0 clear) contains weak references and may have both fixed and
> indexable fields.  (Unless the object contains only fixed fields then you
> have to follow the class pointer and look in the class's "instanceSize"
> field to find out how many fixed fields are in it.)
>
> If bit 3 is set (byte object) then bit 2 tells you whether it's a compiled
> method (set means it's compiled method).  Methods start with an extra
> header word (look in class CompiledMethod to see what it contains)
> followed by zero or more real pointers (the literals of the method).
> After the pointers they turn into byte objects again.  Bits 1 and 0 (of
> any byte object) are the number of bytes by which the size header (or size
> field in the base header) is too large (since a bytes object might be 0,
> 1, 2 or 3 bytes short of an integral number of words long).
>
> To summarise, if we consider the format as an integer from 0 to 15, we
> get:
>
> 0     0000 no fields
> 1     0001 fixed fields only (all containing pointers)
> 2     0010 indexable fields only (all containing pointers)
> 3     0011 both fixed and indexable fields (all containing pointers)
> 4     0100 both fixed and indexable weak fields (all containing pointers).
> 5     0101 unused
> 6     0110 indexable word fields only (no pointers)
> 7     0111 unused
> 8-11  10xx indexable byte fields only (no pointers)
> 12-15 11xx compiled methods: # of literal oops specified in method header
>
> > Where can I find further detailed information about this 'object
format'.
>
> Browse class ObjectMemory in the image, and the object access primitives
> in class Interpreter.
>
> You might also find the following useful:
>
>   http://www-sor.inria.fr/~piumarta/esug98/slides.ps.gz
>
> starting around page 33.
>
> Regards,
> Ian
>
>
>
>
>