lib/hweight.c

   1 #include <linux/module.h>
   2 #include <asm/types.h>
   3
   4 /**
   5  * hweightN - returns the hamming weight of a N-bit word
   6  * @x: the word to weigh
   7  *
   8  * The Hamming Weight of a number is the total number of bits set in it.
   9  */
  10
  11 unsigned int hweight32(unsigned int w)
  12 {
  13         unsigned int res = w - ((w >> 1) & 0x55555555);
  14         res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
  15         res = (res + (res >> 4)) & 0x0F0F0F0F;
  16         res = res + (res >> 8);
  17         return (res + (res >> 16)) & 0x000000FF;
  18 }
  19 EXPORT_SYMBOL(hweight32);
  20
  21 unsigned int hweight16(unsigned int w)
  22 {
  23         unsigned int res = w - ((w >> 1) & 0x5555);
  24         res = (res & 0x3333) + ((res >> 2) & 0x3333);
  25         res = (res + (res >> 4)) & 0x0F0F;
  26         return (res + (res >> 8)) & 0x00FF;
  27 }
  28 EXPORT_SYMBOL(hweight16);
  29
  30 unsigned int hweight8(unsigned int w)
  31 {
  32         unsigned int res = w - ((w >> 1) & 0x55);
  33         res = (res & 0x33) + ((res >> 2) & 0x33);
  34         return (res + (res >> 4)) & 0x0F;
  35 }
  36 EXPORT_SYMBOL(hweight8);
  37
  38 unsigned long hweight64(__u64 w)
  39 {
  40 #if BITS_PER_LONG == 32
  41         return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w);
  42 #elif BITS_PER_LONG == 64
  43         __u64 res = w - ((w >> 1) & 0x5555555555555555ul);
  44         res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
  45         res = (res + (res >> 4)) & 0x0F0F0F0F0F0F0F0Ful;
  46         res = res + (res >> 8);
  47         res = res + (res >> 16);
  48         return (res + (res >> 32)) & 0x00000000000000FFul;
  49 #else
  50 #error BITS_PER_LONG not defined
  51 #endif
  52 }
  53 EXPORT_SYMBOL(hweight64);