Root/lib/memweight.c

1#include <linux/export.h>
2#include <linux/bug.h>
3#include <linux/bitmap.h>
4
5/**
6 * memweight - count the total number of bits set in memory area
7 * @ptr: pointer to the start of the area
8 * @bytes: the size of the area
9 */
10size_t memweight(const void *ptr, size_t bytes)
11{
12    size_t ret = 0;
13    size_t longs;
14    const unsigned char *bitmap = ptr;
15
16    for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
17            bytes--, bitmap++)
18        ret += hweight8(*bitmap);
19
20    longs = bytes / sizeof(long);
21    if (longs) {
22        BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
23        ret += bitmap_weight((unsigned long *)bitmap,
24                longs * BITS_PER_LONG);
25        bytes -= longs * sizeof(long);
26        bitmap += longs * sizeof(long);
27    }
28    /*
29     * The reason that this last loop is distinct from the preceding
30     * bitmap_weight() call is to compute 1-bits in the last region smaller
31     * than sizeof(long) properly on big-endian systems.
32     */
33    for (; bytes > 0; bytes--, bitmap++)
34        ret += hweight8(*bitmap);
35
36    return ret;
37}
38EXPORT_SYMBOL(memweight);
39

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