From: Rich Felker <dalias@libc.org>
To: Alexander Monakov <amonakov@ispras.ru>
Cc: musl@lists.openwall.com
Subject: Re: [musl] [C23 new stdlib 2/4] C23: add the memalignment function
Date: Thu, 1 Jun 2023 15:08:04 -0400 [thread overview]
Message-ID: <20230601190803.GL4163@brightrain.aerifal.cx> (raw)
In-Reply-To: <917e05a1-26b9-5e13-006f-85518348c9e9@ispras.ru>
On Thu, Jun 01, 2023 at 04:35:04PM +0300, Alexander Monakov wrote:
>
> On Thu, 25 May 2023, Jₑₙₛ Gustedt wrote:
>
> > Rich,
> >
> > on Wed, 24 May 2023 17:28:35 -0400 you (Rich Felker <dalias@libc.org>)
> > wrote:
> >
> > > There's a more efficient implementation of this function which does
> > > not depend on __builtin_ctzll (which we don't): p^(p-1)&p
> >
> > yes, nice
> >
> > If you have other such nice formulas for some of the interfaces in
> > <stdbit.h>, please let me know. They are hard to find in search
> > engines.
>
> It seems this was unanswered. Hacker's Delight by Henry Warren offers
> a lot of material on such topics. For this particular question it also
> gives the efficient implementation: 'p & -p'.
Wow, I don't know why I didn't realize this being that p&-p is a
common pattern I use... Somehow I didn't see that it was the same
operation.
Rich
next prev parent reply other threads:[~2023-06-01 19:08 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-24 19:38 [musl] [C23 new stdlib 0/4] changes in stdlib.h Jens Gustedt
2023-05-24 19:38 ` [musl] [C23 new stdlib 1/4] C23: add the new interfaces free_sized and free_aligned_sized for stdlib.h Jens Gustedt
2023-05-24 21:31 ` Rich Felker
2023-05-25 9:38 ` Jₑₙₛ Gustedt
2023-05-25 12:57 ` Rich Felker
2023-05-24 19:38 ` [musl] [C23 new stdlib 2/4] C23: add the memalignment function Jens Gustedt
2023-05-24 21:28 ` Rich Felker
2023-05-24 22:12 ` Rich Felker
2023-05-25 9:17 ` Jₑₙₛ Gustedt
2023-05-25 9:16 ` Jₑₙₛ Gustedt
2023-05-25 9:42 ` NRK
2023-05-25 13:07 ` Rich Felker
2023-05-25 14:05 ` Jₑₙₛ Gustedt
2023-05-25 14:34 ` Rich Felker
2023-05-25 15:22 ` Jₑₙₛ Gustedt
2023-06-01 13:35 ` Alexander Monakov
2023-06-01 19:08 ` Rich Felker [this message]
2023-06-02 8:07 ` Jₑₙₛ Gustedt
2023-06-02 8:03 ` Jₑₙₛ Gustedt
2023-06-02 8:37 ` Alexander Monakov
2023-05-24 19:38 ` [musl] [C23 new stdlib 3/4] C23: implement the new strfrom[dfl] functions Jens Gustedt
2023-05-24 21:42 ` Rich Felker
2023-05-24 19:38 ` [musl] [C23 new stdlib 4/4] C23: add the new include guard to stdlib.h Jens Gustedt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20230601190803.GL4163@brightrain.aerifal.cx \
--to=dalias@libc.org \
--cc=amonakov@ispras.ru \
--cc=musl@lists.openwall.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).