Re: Thinking about changed buffers

[Lars Magne Ingebrigtsen]

Lars Magne Ingebrigtsen <address@hidden> writes:

> 1) Speed.

And I had an idea here, too.  :-)  `buffer-modified-p' is today just
this simple integer comparison:

DEFUN ("buffer-modified-p", Fbuffer_modified_p, Sbuffer_modified_p,
[...]
  return BUF_SAVE_MODIFF (buf) < BUF_MODIFF (buf) ? Qt : Qnil;
}

How could it look under a hashey regime?  Pseudoish code coming up:

{
  if (BUF_SAVE_MODIFF (buf) == BUF_MODIFF (buf))
    return Qnil;
  if (BUF_SAVE_HASHED_SIZE (buf) != BUF_HASHED_SIZE (buf))
    return Qt;
  same = string_equal(buffer_hash (buf), buf->save_hash);
  if (! NILP (same))
    buf->text->save_modiff = buf->text->modiff;
  return same;
}

Uhm...  is that correct?  *squints*  Perhaps.

Anyway, if we do it this way (that is, keep the modiff counter around),
we can short circuit the hash calculation like, almost always.  It would
only be necessary (the first time per ... time) the buffer reaches the
same size that it used to be.

That is, it would basically happen in the "insert an 'a' and then delete
the 'a'" case, but very seldom otherwise, so `buffer-modified-p' would
be almost as fast as it usually is.

Now I'm kinda starting to think that this isn't just feasible, but
possible in practice, too.  :-)

I might be totally wrong, though.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no