Re: Reading portions of large files

[David Kastrup]

"Eli Zaretskii" <eliz@is.elta.co.il> writes:

> > From: David Kastrup <dak@gnu.org>
> > Newsgroups: gnu.emacs.help
> > Date: 10 Jan 2003 21:51:49 +0100
> > 
> > BTW, would it be terribly complicated to extend the range of Lisp
> > integers to 31bit?
> 
> It's not terribly hard, but IIRC the current consensus among the Emacs
> maintainers is that it's not important enough to do that because
> before long all machines will have 64-bit compilers.
> 
> Perhaps this should be discussed again on the developers' list.
> 
> > Integers don't need any garbage collection or tag bits per se.
> 
> They need to be distinguishable from other Lisp types, so their tag
> bitfield cannot have an arbitrary bit pattern.

Yes, but a single bit is sufficient for that distinction.  This could
even speed up operations, since the sign bit is a candidate that can
be rather quickly checked.

Something like
  if (x < 0)
will establish that something is an integer,
  (x + 0x40000000)
will yield the value of the integer, and
  (x | 0x8000000)
will convert an integer back to a Lisp number.

I don't know whether an integer Lisp object needs to be identical to
an integer.  If it does, then the above needs an offset of 0x40000000
everywhere, of course.

> > Emacs has a most-positive-fixnum of 134217727, while XEmacs has
> > 1073741823, more than 8 times as much.  So it would appear to be
> > possible in theory.
> 
> IIRC, the XEmacs way requires extensive changes in how Emacs works,
> but I don't remember the details.

No clue about that.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum