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Commit 639b9e34 authored by Akinobu Mita's avatar Akinobu Mita Committed by Linus Torvalds
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string: introduce memweight() 



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.

[akpm@linux-foundation.org: rename `w' to `ret']
Signed-off-by: default avatarAkinobu Mita <akinobu.mita@gmail.com>
Cc: Anders Larsen <al@alarsen.net>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Tony Luck <tony.luck@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f7f95056

include/linux/string.h

+3 −0
Original line number Diff line number Diff line
@@ -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_ */

lib/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -22,7 +22,7 @@ lib-y += kobject.o klist.o 
obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \

	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \

	 string_helpers.o gcd.o lcm.o list_sort.o uuid.o flex_array.o \

	 bsearch.o find_last_bit.o find_next_bit.o llist.o

	 bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o

obj-y += kstrtox.o

obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o

lib/memweight.c

0 → 100644
+38 −0
Original line number Diff line number Diff line 
#include <linux/export.h>

#include <linux/bug.h>

#include <linux/bitmap.h>



/**

 * 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 ret = 0;

	size_t longs;

	const unsigned char *bitmap = ptr;



	for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);

			bytes--, bitmap++)

		ret += hweight8(*bitmap);



	longs = bytes / sizeof(long);

	if (longs) {

		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);

		ret += bitmap_weight((unsigned long *)bitmap,

				longs * BITS_PER_LONG);

		bytes -= longs * sizeof(long);

		bitmap += longs * sizeof(long);

	}

	/*

	 * The reason that this last loop is distinct from the preceding

	 * bitmap_weight() call is to compute 1-bits in the last region smaller

	 * than sizeof(long) properly on big-endian systems.

	 */

	for (; bytes > 0; bytes--, bitmap++)

		ret += hweight8(*bitmap);



	return ret;

}

EXPORT_SYMBOL(memweight);