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  */
  10 size_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 }
  38 EXPORT_SYMBOL(memweight);