[PATCH v2 01/10] string: introduce memweight

[Akinobu Mita]

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);
+
+	return w;
+}
+EXPORT_SYMBOL(memweight);
-- 
1.7.7.6

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