Re: Bit shift oddity?

[Gregory Heytings]

> 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'.