Re: USE_LSB_TAG and MS-DOS

["Eli Zaretskii" <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: 16 May 2004 19:40:23 -0400
> 
> > Btw, the way DECL_ALIGN and USE_LSB_TAG are defined on lisp.h doesn't
> > leave any elegant way for specific platforms to turn that off without
> > cluttering lisp.h with ugly OS-specific #ifdef's.  Perhaps we should
> > devise a cleaner way.
> 
> It was devised in the hope that it will only be turned on where it's safe.
> Obviously, that's not the way it works, but at least it *should* work that
> way, so I think we're just hitting a bug.
> After all, all we need is to make sure pointers are multiples of 8.
> GNU malloc guarantees that AFAIK for malloced objects and DECL_ALIGN allows
> to get the same guarantee for static objects, so if we have both the only
> reasonf ro USE_LSB_TAG to fail is a bug, right?

I still think we should have an easy way to force or disable use of
LSB tags.  lisp.h already checks MAC_OSX for that, which is not nice
IMHO.

How about if USE_LSB_TAG's value will tell this, viz

  - if USE_LSB_TAG is defined to a non-zero value, always use LSB tags
  - if it is zero, don't use them
  - if it's undefined, lisp.h will use the current method to define
    it to either zero or 1

With this setup, Mac OSX could #define USE_LSB_TAG 1 in its config
file, and be done with that.