]> git.kernelconcepts.de Git - karo-tx-linux.git/commitdiff
string: introduce memweight()
authorAkinobu Mita <akinobu.mita@gmail.com>
Sat, 21 Jul 2012 00:54:50 +0000 (10:54 +1000)
committerStephen Rothwell <sfr@canb.auug.org.au>
Wed, 25 Jul 2012 03:53:17 +0000 (13:53 +1000)
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@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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
include/linux/string.h
lib/string.c

index e033564f10baec5b9b39a75c29f956f5d512e7c4..ffe0442e18d2f4e2d7b8d8eb8f22ffbc532e67e4 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 e5878de4f1013ddbdd3db07d1fca2bcc3a692a7c..e4671869065d36d6ba8853c9464fef874b4ed0d1 100644 (file)
@@ -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 +825,38 @@ 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);
+       }
+       /*
+        * 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++)
+               w += hweight8(*bitmap);
+
+       return w;
+}
+EXPORT_SYMBOL(memweight);