lib/memweight.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/export.h>
   3 #include <linux/bug.h>
   4 #include <linux/bitmap.h>
   5
   6 /**
   7  * memweight - count the total number of bits set in memory area
   8  * @ptr: pointer to the start of the area
   9  * @bytes: the size of the area
  10  */
  11 size_t memweight(const void *ptr, size_t bytes)
  12 {
  13         size_t ret = 0;
  14         size_t longs;
  15         const unsigned char *bitmap = ptr;
  16
  17         for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
  18                         bytes--, bitmap++)
  19                 ret += hweight8(*bitmap);
  20
  21         longs = bytes / sizeof(long);
  22         if (longs) {
  23                 BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
  24                 ret += bitmap_weight((unsigned long *)bitmap,
  25                                 longs * BITS_PER_LONG);
  26                 bytes -= longs * sizeof(long);
  27                 bitmap += longs * sizeof(long);
  28         }
  29         /*
  30          * The reason that this last loop is distinct from the preceding
  31          * bitmap_weight() call is to compute 1-bits in the last region smaller
  32          * than sizeof(long) properly on big-endian systems.
  33          */
  34         for (; bytes > 0; bytes--, bitmap++)
  35                 ret += hweight8(*bitmap);
  36
  37         return ret;
  38 }
  39 EXPORT_SYMBOL(memweight);