#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);