linux-kernel - Re: [PATCH] hpfs: Use hweight32

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Date:	Sun, 15 Nov 2009 08:16:31 +0100 (CET)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Akinobu Mita <akinobu.mita@...il.com>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] hpfs: Use hweight32



On Fri, 13 Nov 2009, Andrew Morton wrote:

> On Fri, 13 Nov 2009 16:07:08 +0900
> Akinobu Mita <akinobu.mita@...il.com> wrote:
> 
> > Use hweight32 instead of counting for each bit
> > 
> > Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> > Cc: Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > ---
> >  fs/hpfs/super.c |    7 ++-----
> >  1 files changed, 2 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/hpfs/super.c b/fs/hpfs/super.c
> > index f2feaa0..cf6fe4a 100644
> > --- a/fs/hpfs/super.c
> > +++ b/fs/hpfs/super.c
> > @@ -119,11 +119,8 @@ unsigned hpfs_count_one_bitmap(struct super_block *s, secno secno)
> >  	unsigned i, count;
> >  	if (!(bits = hpfs_map_4sectors(s, secno, &qbh, 4))) return 0;
> >  	count = 0;
> > -	for (i = 0; i < 2048 / sizeof(unsigned); i++) {
> > -		unsigned b; 
> > -		if (!bits[i]) continue;
> > -		for (b = bits[i]; b; b>>=1) count += b & 1;
> > -	}
> > +	for (i = 0; i < 2048 / sizeof(unsigned); i++)
> > +		count += hweight32(bits[i]);
> >  	hpfs_brelse4(&qbh);
> >  	return count;
> 
> Could actualy use bitmap_weight() here.
> 
> It's a bit naughty, because bitmap_weight() operates on long*'s, but it
> will work OK.
> 
> Shrug.

... and add support for popcnt, so that it's optimized on AMD CPUs.

Mikulas
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