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Date: Tue, 24 Mar 2015 15:53:03 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Yury Norov <yury.norov@gmail.com>
Cc: linux@horizon.com, klimov.linux@gmail.com, linux@rasmusvillemoes.dk,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] lib: bitmap_[empty,full]: remove code duplication
Message-Id: <20150324155303.f5ced0c3395e315319a0c9e6@linux-foundation.org>
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On Mon, 16 Mar 2015 20:56:39 +0300 Yury Norov <yury.norov@gmail.com> wrote:

> Function 'bitmap_empty' has it's own implementation.
> But it's clearly as simple as:
> 	"find_first_bit(src, nbits) == nbits"
> The same is true for 'bitmap_full'.
> 
> Underscored versions of 'bitmap_[empty,full]' are not
> needed anymore and so removed too.
> 
> Boot-tested on Core i7-2630QM.
> 
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -285,18 +285,12 @@ static inline int bitmap_subset(const unsigned long *src1,
>  
>  static inline int bitmap_empty(const unsigned long *src, unsigned nbits)
>  {
> -	if (small_const_nbits(nbits))
> -		return ! (*src & BITMAP_LAST_WORD_MASK(nbits));
> -	else
> -		return __bitmap_empty(src, nbits);
> +	return find_first_bit(src, nbits) == nbits;
>  }

But we lost the small_const_nbits() optimization, and that will be a
common case.

Would it be better to do

	if (small_const_nbits(...))
		...
	else
		find_first_bit(...);

?