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Message-ID: <d86ad462-fb4c-4768-b060-201511f9ff64@rasmusvillemoes.dk>
Date:   Fri, 8 Jul 2022 10:26:04 +0200
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Subject: Re: [PATCH 1/5] lib: add find_nth(,and,andnot)_bit()
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To:     Yury Norov <yury.norov@gmail.com>
Cc:     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?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= <toke@redhat.com>
References: <20220706182300.70862-1-yury.norov@gmail.com>
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 <423c4368-0a1c-792c-2637-768532fc7782@rasmusvillemoes.dk>
 <YsdKMQzUFVwIaqtJ@yury-laptop>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
In-Reply-To: <YsdKMQzUFVwIaqtJ@yury-laptop>
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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