linux-kernel - Re: [RFC PATCH 1/2] bits: introduce ffs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <c63b2d4a-985c-442b-a171-e08059bdca3a@app.fastmail.com>
Date: Fri, 09 Jan 2026 18:01:02 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Petr Tesarik" <ptesarik@...e.com>, "Yury Norov" <yury.norov@...il.com>,
 "Rasmus Villemoes" <linux@...musvillemoes.dk>
Cc: "Richard Henderson" <richard.henderson@...aro.org>,
 "Matt Turner" <mattst88@...il.com>,
 "Magnus Lindholm" <linmag7@...il.com>,
 "Vineet Gupta" <vgupta@...nel.org>,
 "Geert Uytterhoeven" <geert@...ux-m68k.org>,
 "Maciej W. Rozycki" <macro@...am.me.uk>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Madhavan Srinivasan" <maddy@...ux.ibm.com>,
 "Michael Ellerman" <mpe@...erman.id.au>,
 "Heiko Carstens" <hca@...ux.ibm.com>,
 "Vasily Gorbik" <gor@...ux.ibm.com>,
 "Alexander Gordeev" <agordeev@...ux.ibm.com>,
 "Chris Zankel" <chris@...kel.net>, "Max Filippov" <jcmvbkbc@...il.com>,
 "Patrik Jakobsson" <patrik.r.jakobsson@...il.com>,
 "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
 "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>,
 "Dave Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>,
 "Robin Murphy" <robin.murphy@....com>, "Joerg Roedel" <joro@...tes.org>,
 "Will Deacon" <will@...nel.org>, "Jakub Kicinski" <kuba@...nel.org>,
 "Andrew Lunn" <andrew+netdev@...n.ch>,
 "David S . Miller" <davem@...emloft.net>,
 "Eric Dumazet" <edumazet@...gle.com>, "Paolo Abeni" <pabeni@...hat.com>,
 "Oliver Neukum" <oliver@...kum.org>,
 "Kuan-Wei Chiu" <visitorckw@...il.com>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Marcel Holtmann" <marcel@...tmann.org>,
 "Johan Hedberg" <johan.hedberg@...il.com>,
 "Luiz Augusto von Dentz" <luiz.dentz@...il.com>,
 "Pablo Neira Ayuso" <pablo@...filter.org>,
 "Florian Westphal" <fw@...len.de>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] bits: introduce ffs_val()

On Fri, Jan 9, 2026, at 17:37, Petr Tesarik wrote:

> + * Returns:
> + * least significant non-zero bit, 0 if all bits are zero
> + */
> +#define ffs_val(x)			\
> +({					\
> +	const typeof(x) val__ = (x);	\
> +	val__ & -val__;			\
> +})

This looks good to me, but I'd suggest using 'const auto val__'
instead of typeof(), to reduce expanding complex arguments twice.

    Arnd