(elisp)Object Internals

(elisp)Object Internals

[Luc Teirlinck]

Is the following quote from `(elisp)Object Internals' still
"essentially accurate"?

    Depending on the operating system and type of machine for which you
    compile Emacs, twenty-eight bits are used to address the object, and
    the remaining four bits are used for a GC mark bit and the tag that
    identifies the object's type.

I know that this is not true for integers any more, but is it still
true for most other objects?

Sincerely,

Luc.

Re: (elisp)Object Internals

[Luc Teirlinck]

I believe I understand now that the quote from `(elisp)Object
Internals' should be changed to:

    Depending on the operating system and type of machine for which
    you compile Emacs, twenty-nine bits are used to address the
    object, and the remaining three bits are used for a GC mark bit and
    the tag that identifies the object's type.

Is this accurate?

Sincerely,

Luc.

Re: (elisp)Object Internals

[Kim F. Storm]

Luc Teirlinck <teirllm@dms.auburn.edu> writes:

> I believe I understand now that the quote from `(elisp)Object
> Internals' should be changed to:
> 
>     Depending on the operating system and type of machine for which
>     you compile Emacs, twenty-nine bits are used to address the
>     object, and the remaining three bits are used for a GC mark bit and
>     the tag that identifies the object's type.
> 
> Is this accurate?

I think so.  

But I don't know if there are systems where this doesn't apply.

When I see "Depending on..." in a text, I would expect to see various
alternatives following that.  In this case there is nothing in the
text that suggests it actually depends on anything...

Perhaps a "may" in the right spot would is needed?

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk

Re: (elisp)Object Internals

[Luc Teirlinck]

Kim Storm wrote:

   But I don't know if there are systems where this doesn't apply.

What about 64 bit systems?

   When I see "Depending on..." in a text, I would expect to see various
   alternatives following that.

The entire description of the C code internals in the Elisp manual is
not very detailed.

Sincerely,

Luc.

Re: (elisp)Object Internals

[Luc Teirlinck]

Kim Storm wrote:

   When I see "Depending on..." in a text, I would expect to see various
   alternatives following that.  In this case there is nothing in the
   text that suggests it actually depends on anything...

I should have quoted the entire paragraph:

    GNU Emacs Lisp manipulates many different types of data.  The
    actual data are stored in a heap and the only access that programs
    have to it is through pointers.  Pointers are thirty-two bits wide
    in most implementations.  Depending on the operating system and
    type of machine for which you compile Emacs, twenty-eight bits are
    used to address the object, and the remaining four bits are used
    for a GC mark bit and the tag that identifies the object's type.

To me, that suggests that one thing it depends on is pointer size.

Sincerely,

Luc.

Re: (elisp)Object Internals

[Richard Stallman]

    >     Depending on the operating system and type of machine for which
    >     you compile Emacs, twenty-nine bits are used to address the
    >     object, and the remaining three bits are used for a GC mark bit and
    >     the tag that identifies the object's type.
    > 
    > Is this accurate?

    I think so.  

    But I don't know if there are systems where this doesn't apply.

It is only meant to describe the most common systems, not all
systems.

Re: (elisp)Object Internals

[Stefan Monnier]

> I believe I understand now that the quote from `(elisp)Object
> Internals' should be changed to:

>     Depending on the operating system and type of machine for which
>     you compile Emacs, twenty-nine bits are used to address the
>     object, and the remaining three bits are used for a GC mark bit and
>     the tag that identifies the object's type.

Actually, the recent change was to remove the mark bit, so something like
the following would be better:

     Depending on the operating system and type of machine for which
     you compile Emacs, twenty-nine bits are used to address the
     object, and the remaining three bits are used for
     the tag that identifies the object's type.


-- Stefan

Re: (elisp)Object Internals

[Luc Teirlinck]

Stefan Monnier wrote:

   Actually, the recent change was to remove the mark bit, so something like
   the following would be better:

	Depending on the operating system and type of machine for which
	you compile Emacs, twenty-nine bits are used to address the
	object, and the remaining three bits are used for
	the tag that identifies the object's type.

Thanks for clarifying.  I will use the text you suggested.

Sincerely,

Luc.