Who's flying the plane ?

Cheers,

PhiHo.

----- Original Message -----
From: "Alan Kay" <Alan.Kay at squeakland.org>
To: <squeak-dev at lists.squeakfoundation.org>
Sent: Sunday, October 13, 2002 7:51 PM
Subject: Re: Object Format


> Depends on who's flying the plane ...
>
> Cheers,
>
> Alan
> -----
>
> At 6:47 PM -0400 10/13/02, PhiHo Hoang wrote:
> >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
> >>
> >>
> >>
> >>
> >>
>
>
> --
>