On Sat, 9 Jun 2012 09:50:30 +0900
Akinobu Mita <akinobu.m...@gmail.com> 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.
> + 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);
_
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