On Mon 04-06-12 20:46:14, Akinobu Mita wrote: > 2012/6/4 Jan Kara <jack@xxxxxxx>: > > 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.mita@xxxxxxxxx> > >> Cc: Anders Larsen <al@xxxxxxxxxxx> > >> Cc: Alasdair Kergon <agk@xxxxxxxxxx> > >> Cc: dm-devel@xxxxxxxxxx > >> Cc: linux-fsdevel@xxxxxxxxxxxxxxx > >> Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > >> Cc: linux-media@xxxxxxxxxxxxxxx > >> Cc: Mark Fasheh <mfasheh@xxxxxxxx> > >> Cc: Joel Becker <jlbec@xxxxxxxxxxxx> > >> Cc: ocfs2-devel@xxxxxxxxxxxxxx > >> Cc: Jan Kara <jack@xxxxxxx> > >> Cc: linux-ext4@xxxxxxxxxxxxxxx > >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > >> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx> > >> Cc: "Theodore Ts'o" <tytso@xxxxxxx> > >> Cc: Matthew Wilcox <matthew@xxxxxx> > >> --- > >> > >> 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...). > > This last loop is necessary for big-endian architecture. > if bytes % sizeof(long) != 0, bitmap_weight() counts one-bits in wrong > byte-field > of the last long word. Ah, right. OK. Add this to the comment before the loop please. You save yourself some explanations :) Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html