Date:   Sun, 28 Nov 2021 19:10:20 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Yury Norov <yury.norov@...il.com>
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Subject: Re: [PATCH 2/9] lib/bitmap: implement bitmap_{empty,full} with
 bitmap_weight_eq()

On Sat, Nov 27, 2021 at 07:56:57PM -0800, Yury Norov wrote:
> Now as we have bitmap_weight_eq(), switch bitmap_full() and
> bitmap_empty() to using it.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
>  include/linux/bitmap.h | 26 ++++++++++----------------
>  1 file changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> index 996041f771c8..2d951e4dc814 100644
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -386,22 +386,6 @@ static inline int bitmap_subset(const unsigned long *src1,
>  		return __bitmap_subset(src1, src2, nbits);
>  }
>  
> -static inline bool bitmap_empty(const unsigned long *src, unsigned nbits)
> -{
> -	if (small_const_nbits(nbits))
> -		return ! (*src & BITMAP_LAST_WORD_MASK(nbits));
> -
> -	return find_first_bit(src, nbits) == nbits;
> -}

Since this is supposed to be an optimization, I would go all the way and
replace this with the trivial implementation instead:

bool bitmap_empty(long *bits, size_t nbits)
{
	for (; nbits >= BITS_PER_LONG; ++bits, nbits -= BITS_PER_LONG)
		if (*bits)
			return false;

	if (nbits && *bits & BITMAP_LAST_WORD_MASK(nbits))
		return false;

	return true;
}
 
Best Regards
Michał Mirosław

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