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

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Date:   Fri, 8 Jul 2022 10:26:04 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Yury Norov <yury.norov@...il.com>
Cc:     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 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.

Rasmus