linux-kernel - Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot

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Date:   Thu, 18 Aug 2022 10:08:20 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Mel Gorman <mgorman@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Tony Luck <tony.luck@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Gal Pressman <gal@...dia.com>, Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

On Wed, 17 Aug 2022 18:58:08 +0100
Valentin Schneider <vschneid@...hat.com> wrote:

> +#ifndef find_next_andnot_bit
> +/**
> + * find_next_andnot_bit - find the next set bit in one memory region
> + *                        but not in the other
> + * @addr1: The first address to base the search on
> + * @addr2: The second address to base the search on
> + * @size: The bitmap size in bits
> + * @offset: The bitnumber to start searching at
> + *
> + * Returns the bit number for the next set bit
> + * If no bits are set, returns @size.

Can we make the above documentation more descriptive. Because I read this
three times, and I still have no idea what it does.

The tag line sounds like the nursery song "One of these things is not like
the others".

-- Steve


> + */
> +static inline
> +unsigned long find_next_andnot_bit(const unsigned long *addr1,
> +		const unsigned long *addr2, unsigned long size,
> +		unsigned long offset)
> +{
> +	if (small_const_nbits(size)) {
> +		unsigned long val;
> +
> +		if (unlikely(offset >= size))
> +			return size;
> +
> +		val = *addr1 & ~*addr2 & GENMASK(size - 1, offset);
> +		return val ? __ffs(val) : size;
> +	}
> +
> +	return _find_next_bit(addr1, addr2, size, offset, 0UL, ~0UL, 0);
>  }
>  #endif