3 files changed, 42 insertions, 1 deletions

diff --git a/include/linux/string.h b/include/linux/string.h
index e033564f10ba..ffe0442e18d2 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/Makefile b/lib/Makefile
index 8c31a0cb75e9..df663cc05c73 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -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
index 000000000000..e35fc8771893
--- /dev/null
+++ b/lib/memweight.c
@@ -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);