From: Matthew Wilcox <matthew@wil.cx>
To: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jan Kara <jack@suse.cz>,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
Anders Larsen <al@alarsen.net>, Alasdair Kergon <agk@redhat.com>,
dm-devel@redhat.com, linux-fsdevel@vger.kernel.org,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
linux-media@vger.kernel.org, Mark Fasheh <mfasheh@suse.com>,
Joel Becker <jlbec@evilplan.org>,
ocfs2-devel@oss.oracle.com, linux-ext4@vger.kernel.org,
Andreas Dilger <adilger.kernel@dilger.ca>,
"Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [PATCH 01/10] string: introduce memweight
Date: Wed, 23 May 2012 07:16:00 -0600 [thread overview]
Message-ID: <20120523131559.GA7064@parisc-linux.org> (raw)
In-Reply-To: <CAC5umyi=ridqRZGGh0+_xw0-GCN+69B33Qz82-9x4dVODGGx6w@mail.gmail.com>
On Wed, May 23, 2012 at 09:12:18PM +0900, Akinobu Mita wrote:
> size_t memweight(const void *ptr, size_t bytes)
Why should this return size_t instead of unsigned long?
> {
> size_t w = 0;
> size_t longs;
> const unsigned char *bitmap = ptr;
>
> for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
> bytes--, bitmap++)
> w += hweight8(*bitmap);
>
> longs = bytes / sizeof(long);
> BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
> w += bitmap_weight((unsigned long *)bitmap, longs * BITS_PER_LONG);
> bytes -= longs * sizeof(long);
> bitmap += longs * sizeof(long);
>
> for (; bytes > 0; bytes--, bitmap++)
> w += hweight8(*bitmap);
>
> return w;
> }
bitmap_weight copes with a bitmask that isn't a multiple of BITS_PER_LONG
in size already. So I think this can be done as:
unsigned long memweight(const void *s, size_t n)
{
const unsigned char *ptr = s;
unsigned long r = 0;
while (n > 0 && (unsigned long)ptr % sizeof(long)) {
r += hweight8(*ptr);
n--;
ptr++;
}
BUG_ON(n >= INT_MAX / 8)
return r + bitmap_weight((unsigned long *)ptr, n * 8);
}
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
next prev parent reply other threads:[~2012-05-23 13:16 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-20 13:23 [PATCH 01/10] string: introduce memweight Akinobu Mita
2012-05-20 13:23 ` [PATCH 02/10] minixfs: use memweight() Akinobu Mita
2012-05-20 13:23 ` [PATCH 03/10] qnx4fs: " Akinobu Mita
2012-05-20 15:34 ` Anders Larsen
2012-05-21 11:59 ` Akinobu Mita
2012-05-20 13:23 ` [PATCH 04/10] dm-log: " Akinobu Mita
2012-05-20 13:23 ` [PATCH 05/10] affs: " Akinobu Mita
2012-05-20 13:23 ` [PATCH 06/10] video/uvc: " Akinobu Mita
2012-05-20 20:46 ` Laurent Pinchart
2012-05-21 12:03 ` Akinobu Mita
2012-05-21 12:18 ` Laurent Pinchart
2012-05-20 13:23 ` [PATCH 07/10] ocfs2: " Akinobu Mita
2012-05-20 13:23 ` [PATCH 08/10] ext2: " Akinobu Mita
2012-05-20 13:23 ` [PATCH 09/10] ext3: " Akinobu Mita
2012-05-20 13:23 ` [PATCH 10/10] ext4: " Akinobu Mita
2012-05-23 9:21 ` [PATCH 01/10] string: introduce memweight Jan Kara
2012-05-23 12:12 ` Akinobu Mita
2012-05-23 12:29 ` Jan Kara
2012-05-23 13:16 ` Matthew Wilcox [this message]
2012-05-24 11:54 ` Akinobu Mita
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