From: Alexander Monakov <amonakov@ispras.ru>
To: musl@lists.openwall.com
Cc: Rich Felker <dalias@libc.org>
Subject: Re: [musl] [C23 new stdlib 2/4] C23: add the memalignment function
Date: Thu, 1 Jun 2023 16:35:04 +0300 (MSK) [thread overview]
Message-ID: <917e05a1-26b9-5e13-006f-85518348c9e9@ispras.ru> (raw)
In-Reply-To: <20230525111653.4b0175d3@inria.fr>
[-- Attachment #1: Type: text/plain, Size: 815 bytes --]
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'.
I looked over the recently posted stdbit.h patch and I don't have anything
to suggest in terms of formulas. The things that would worry me are of a
different nature anyway.
Alexander
next prev parent reply other threads:[~2023-06-01 13:35 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 [this message]
2023-06-01 19:08 ` Rich Felker
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
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