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
>>
>>
>>
>>
>>


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