From: Douglas Lewan <d.lewan2000@gmail.com>
To: Gregory Heytings <ghe@sdf.org>
Cc: help-gnu-emacs <help-gnu-emacs@gnu.org>
Subject: Re: Bit shift oddity?
Date: Mon, 19 Oct 2020 11:19:20 -0400 [thread overview]
Message-ID: <e11d2022-2a9f-64ca-4898-b27f32d29331@gmail.com> (raw)
In-Reply-To: <alpine.NEB.2.22.394.2010191119450453.14045@sdf.lonestar.org>
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)
prev parent reply other threads:[~2020-10-19 15:19 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-19 0:19 Bit shift oddity? Douglas Lewan
2020-10-19 7:06 ` tomas
2020-10-19 7:48 ` Douglas Lewan
2020-10-19 9:01 ` tomas
2020-10-19 15:14 ` Stefan Monnier
2020-10-19 15:30 ` tomas
2020-10-19 9:23 ` Gregory Heytings via Users list for the GNU Emacs text editor
2020-10-19 15:19 ` Douglas Lewan [this message]
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