Re: jit lock sit-for provokes redisplay provokes imenu

[Richard Stallman <rms@gnu.org>]

    >   return BUF_SAVE_MODIFF (buf) < BUF_CHARS_MODIFF (buf) ? Qt : Qnil;

    Isn't this vulnerable to problems when MODIFF wraps around?

If the buffer is modified 1000 times a second, with never a pause, it
could wrap around in 24 days.  If we make the field unsigned, that
would increase to 48 days.

However, the Lisp level representation of this (returned by
buffer-modified-tick) is 3 bits smaller, so it would wrap around in
just 6 days.

We could declare the fields long long at the C level, and then they
would never wrap around (assuming there are no compilers that barf on
long long.)  But we would still have the problem at the Lisp level.

It isn't clear how we could fix this.  Meanwhile,
in practice, I think the problem ever happens.
So I think we should deal with it after the release.