On Sat 02-06-12 22:40:07, Akinobu Mita wrote:
> memweight() is the function that counts the total number of bits set
> in memory area.  Unlike bitmap_weight(), memweight() takes pointer
> and size in bytes to specify a memory area which does not need to be
> aligned to long-word boundary.
> 
> Signed-off-by: Akinobu Mita <akinobu.m...@gmail.com>
> Cc: Anders Larsen <a...@alarsen.net>
> Cc: Alasdair Kergon <a...@redhat.com>
> Cc: dm-de...@redhat.com
> Cc: linux-fsde...@vger.kernel.org
> Cc: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
> Cc: linux-media@vger.kernel.org
> Cc: Mark Fasheh <mfas...@suse.com>
> Cc: Joel Becker <jl...@evilplan.org>
> Cc: ocfs2-de...@oss.oracle.com
> Cc: Jan Kara <j...@suse.cz>
> Cc: linux-e...@vger.kernel.org
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Andreas Dilger <adilger.ker...@dilger.ca>
> Cc: "Theodore Ts'o" <ty...@mit.edu>
> Cc: Matthew Wilcox <matt...@wil.cx>
> ---
> 
> v2: simplify memweight(), adviced by Jan Kara
> 
>  include/linux/string.h |    3 +++
>  lib/string.c           |   32 ++++++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/string.h b/include/linux/string.h
> index e033564..ffe0442 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char 
> *prefix)
>       return strncmp(str, prefix, strlen(prefix)) == 0;
>  }
>  #endif
> +
> +extern size_t memweight(const void *ptr, size_t bytes);
> +
>  #endif /* _LINUX_STRING_H_ */
> diff --git a/lib/string.c b/lib/string.c
> index e5878de..bf4d5a8 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -26,6 +26,7 @@
>  #include <linux/export.h>
>  #include <linux/bug.h>
>  #include <linux/errno.h>
> +#include <linux/bitmap.h>
>  
>  #ifndef __HAVE_ARCH_STRNICMP
>  /**
> @@ -824,3 +825,34 @@ void *memchr_inv(const void *start, int c, size_t bytes)
>       return check_bytes8(start, value, bytes % 8);
>  }
>  EXPORT_SYMBOL(memchr_inv);
> +
> +/**
> + * memweight - count the total number of bits set in memory area
> + * @ptr: pointer to the start of the area
> + * @bytes: the size of the area
> + */
> +size_t memweight(const void *ptr, size_t bytes)
> +{
> +     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);
> +     if (longs) {
> +             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);
  Looking at bitmap_weight() it seems this last loop is not needed. Just
pass to bitmap_weight() bytes*BITS_PER_BYTE. Also generally this function
doesn't seem necessary at all at least for ext2 & ext3 (sorry for not
noticing this earlier...).

                                                                Honza
-- 
Jan Kara <j...@suse.cz>
SUSE Labs, CR
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