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Message-ID: <20120523131559.GA7064@parisc-linux.org>
Date: Wed, 23 May 2012 07:16:00 -0600
From: Matthew Wilcox <matthew@....cx>
To: Akinobu Mita <akinobu.mita@...il.com>
Cc: Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, Anders Larsen <al@...rsen.net>,
Alasdair Kergon <agk@...hat.com>, dm-devel@...hat.com,
linux-fsdevel@...r.kernel.org,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
linux-media@...r.kernel.org, Mark Fasheh <mfasheh@...e.com>,
Joel Becker <jlbec@...lplan.org>, ocfs2-devel@....oracle.com,
linux-ext4@...r.kernel.org,
Andreas Dilger <adilger.kernel@...ger.ca>,
Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH 01/10] string: introduce memweight
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."
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