On Sat, 9 Jun 2012 09:50:30 +0900
Akinobu Mita [off-list ref] wrote:
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.
...
+/**
+ * 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;
Calling the return value "ret" is a useful convention and fits well here.
quoted hunk ↗ jump to hunk
+ 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);
diff -puN lib/string.c~string-introduce-memweight-fix lib/string.c
--- a/lib/string.c~string-introduce-memweight-fix
+++ a/lib/string.c
@@ -833,18 +833,18 @@ EXPORT_SYMBOL(memchr_inv);
*/
size_t memweight(const void *ptr, size_t bytes)
{
- size_t w = 0;
+ size_t ret = 0;
size_t longs;
const unsigned char *bitmap = ptr;
for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
bytes--, bitmap++)
- w += hweight8(*bitmap);
+ ret += hweight8(*bitmap);
longs = bytes / sizeof(long);
if (longs) {
BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
- w += bitmap_weight((unsigned long *)bitmap,
+ ret += bitmap_weight((unsigned long *)bitmap,
longs * BITS_PER_LONG);
bytes -= longs * sizeof(long);
bitmap += longs * sizeof(long);@@ -855,8 +855,8 @@ size_t memweight(const void *ptr, size_t
* than sizeof(long) properly on big-endian systems.
*/
for (; bytes > 0; bytes--, bitmap++)
- w += hweight8(*bitmap);
+ ret += hweight8(*bitmap);
- return w;
+ return ret;
}
EXPORT_SYMBOL(memweight);
_