Emacs also has `most-negative-fixnum' and `most-positive-fixnum' (borrowed
from Common Lisp but now part of the core).

On my 64-bit system (GNU Emacs 30.0.50 on aarch64-apple-darwin22.5.0):

(= (- (expt 2 61)) most-negative-fixnum) ⇒ t
(= (1- (expt 2 61)) most-positive-fixnum) ⇒ t

(Same as on Emanuel's.)
-- 
Simon.

On Wed, Aug 16, 2023 at 1:12 PM Emanuel Berg <incal@dataswamp.org> wrote:

> Gerd Möllmann wrote:
>
> >> I don't know about SBCL, but as for Emacs, refer to the
> >> definition of VALBITS in lisp.h (maybe also the right files
> >> among m/*.h and s/*.h, but I have no idea where they've
> >> disappeared to.)
> >
> > The SBCL I have here, a Homebrew installation, uses the
> > scheme where
> >
> > ....0 -> fixnum
> > ....1   -> other objects (discriminated by additional tag bits)
> >
> > I had the same for Emacs in the branch gerd_int in the
> > 2000s, if memory serves me.
>
> Ah, there is `fixnump' (and `bignump') to test for a specific
> number,
>
>   (fixnump (expt 2 60)) ; t
>   (fixnump (expt 2 61)) ; nil
>
> 2^60 = 1152921504606846976, so that's pretty big.
>
> --
> underground experts united
> https://dataswamp.org/~incal
>
>
>