memweight.c

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#include <linux/export.h>
#include <linux/bug.h>
#include <linux/bitmap.h>

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);