string: introduce memweight()

[cascardo/linux.git] / lib / memweight.c

diff --git a/lib/memweight.c b/lib/memweight.c
new file mode 100644 (file)
index 0000000..e35fc87
--- /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);