string: introduce memweight()
Akinobu Mita [Mon, 30 Jul 2012 21:40:55 +0000 (14:40 -0700)]
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: Akinobu 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/string.h
lib/Makefile
lib/memweight.c [new file with mode: 0644]

index e033564..ffe0442 100644 (file)
@@ -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_ */
index 8c31a0c..df663cc 100644 (file)
@@ -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
 
diff --git a/lib/memweight.c b/lib/memweight.c
new file mode 100644 (file)
index 0000000..e35fc87
--- /dev/null
@@ -0,0 +1,38 @@
+#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);