linux-kernel - Re: [PATCH 1/5] lib: add find_nth(,and,andnot)

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Date:   Fri, 8 Jul 2022 11:12:36 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Yury Norov <yury.norov@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, David Gow <davidgow@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Isabella Basso <isabbasso@...eup.net>,
        Kees Cook <keescook@...omium.org>,
        Keith Busch <kbusch@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH 1/5] lib: add find_nth(,and,andnot)_bit()

On Fri, Jul 8, 2022 at 10:55 AM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> On 07/07/2022 23.03, Yury Norov wrote:
>
> >> And I don't
> >> like that the index is apparently 1-based (and that surprising API isn't
> >> spelled out anywhere).
> >
> > Yeah... My motivation to start counting from 1 is to keep consistency
> > with ffs: __ffs(word) <=> fns(word, 1).
>
> I understand that you're translating that second f in ffs (find First
> set) to a 1. But I disagree that that's necessarily a logical thing to
> do. Everybody understands that (given a C or python or... context) when
> some prose talks about "the first element in an array", it's the one at
> [0]. So I find it much more natural that the set bits in a word are
> enumerated 0, 1, ..., popcount(w)-1.

I agree that here we operate with an array of bits, which naturally
starts from bit 0.

-- 
With Best Regards,
Andy Shevchenko