FreeBSD/Linux Kernel Cross Reference
sys/lib/memweight.c

     #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);

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