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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 8 Jul 2022 11:12:36 +0200
Message-ID: <CAHp75Vfx3RADfU0cm7Y0kYfOtba4K008xZSSVbACRa3OwbAKGw@mail.gmail.com>
Subject: Re: [PATCH 1/5] lib: add find_nth(,and,andnot)_bit()
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc:     Yury Norov <yury.norov@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alexander Lobakin <alexandr.lobakin@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>, David Gow <davidgow@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Isabella Basso <isabbasso@riseup.net>,
        Kees Cook <keescook@chromium.org>,
        Keith Busch <kbusch@kernel.org>,
        Kumar Kartikeya Dwivedi <memxor@gmail.com>,
        Marco Elver <elver@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= <toke@redhat.com>
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On Fri, Jul 8, 2022 at 10:55 AM Rasmus Villemoes
<linux@rasmusvillemoes.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