2012/6/4 Jan Kara <j...@suse.cz>: > 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...).
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. -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html