Re: Bit shift oddity?

[Douglas Lewan]

Nice. Thank you.

On 10/19/20 5:23 AM, Gregory Heytings wrote:
> > I see the following:
> >
> >   ELISP> (= (lsh -1 (lognot 0)) (lsh -2 (lognot 0)))
> >
> >   t
> >
> >   ELISP> (= (lsh -1 (lognot 0)) (lsh -3 (lognot 0)))
> >
> >   nil
> >
> > The first seems odd to me. Is it really what's expected?
>
> Yes, it's what is expected.  The docstring of lsh says:
>
> "(lsh VALUE COUNT) ... If COUNT is negative, shifting is actually to 
> the right. In this case, if VALUE is a negative fixnum treat it as 
> unsigned ..."
>
> -1 (decimal) = 111...111 (binary)
> -2 (decimal) = 111...110 (binary)
>
> If you shift these two numbers to the right, you get the exact same 
> result: 011...111, that is, `most-positive-fixnum'.

--
,Doug
d.lewan2000@gmail.com
(908) 720 7908

You know, it's amazing how much closer to 0 that 8 067 332 is than 15 is. (2020 
Oct 18)