Re: Reading portions of large files

["Stefan Monnier <foo@acm.com>" <monnier+gnu.emacs.help/news/@flint.cs.yale.edu>]

> BTW, would it be terribly complicated to extend the range of Lisp
> integers to 31bit?

Currently a cons cell takes 2 words.  Each word has 3 tag bits and
1 mark bit.  When marking a cons cell, the GC sets the mark bit of the
first word of the cell.  The mark bit of the second word is unused
(i.e. wasted).

Since at least 1 bit of tag is needed, that means that to get 31bit
integers we'd need to move the mark bit somewhere else.  XEmacs decided to
use 3-word cons cells (and I know they're still regularly wondering
whether it was a good idea).  Another approach is to use a separate mark-bit
array.

Lots of trade offs, a fair bit of coding, even more testing, ...
Anybody interested is welcome to tried it out.  My opinion is that maybe it
would be nice, but since the only application I'm aware of is "editing files
between 128MB and 1GB on 32bit systems", I don't think it's worth
the trouble.


        Stefan