text: #include <linux/export.h>
  #include <linux/bitops.h>
  #include <asm/types.h>
  
  /**
   * hweightN - returns the hamming weight of a N-bit word
   * @x: the word to weigh
   *
   * The Hamming Weight of a number is the total number of bits set in it.
   */
  
  unsigned int __sw_hweight32(unsigned int w)
  {
  #ifdef ARCH_HAS_FAST_MULTIPLIER
  	w -= (w >> 1) & 0x55555555;
  	w =  (w & 0x33333333) + ((w >> 2) & 0x33333333);
  	w =  (w + (w >> 4)) & 0x0f0f0f0f;
  	return (w * 0x01010101) >> 24;
  #else
  	unsigned int res = w - ((w >> 1) & 0x55555555);
  	res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
  	res = (res + (res >> 4)) & 0x0F0F0F0F;
  	res = res + (res >> 8);
  	return (res + (res >> 16)) & 0x000000FF;
  #endif
  }
  EXPORT_SYMBOL(__sw_hweight32);
  
  unsigned int __sw_hweight16(unsigned int w)
  {
  	unsigned int res = w - ((w >> 1) & 0x5555);
  	res = (res & 0x3333) + ((res >> 2) & 0x3333);
  	res = (res + (res >> 4)) & 0x0F0F;
  	return (res + (res >> 8)) & 0x00FF;
  }
  EXPORT_SYMBOL(__sw_hweight16);
  
  unsigned int __sw_hweight8(unsigned int w)
  {
  	unsigned int res = w - ((w >> 1) & 0x55);
  	res = (res & 0x33) + ((res >> 2) & 0x33);
  	return (res + (res >> 4)) & 0x0F;
  }
  EXPORT_SYMBOL(__sw_hweight8);
  
  unsigned long __sw_hweight64(__u64 w)
  {
  #if BITS_PER_LONG == 32
  	return __sw_hweight32((unsigned int)(w >> 32)) +
  	       __sw_hweight32((unsigned int)w);
  #elif BITS_PER_LONG == 64
  #ifdef ARCH_HAS_FAST_MULTIPLIER
  	w -= (w >> 1) & 0x5555555555555555ul;
  	w =  (w & 0x3333333333333333ul) + ((w >> 2) & 0x3333333333333333ul);
  	w =  (w + (w >> 4)) & 0x0f0f0f0f0f0f0f0ful;
  	return (w * 0x0101010101010101ul) >> 56;
  #else
  	__u64 res = w - ((w >> 1) & 0x5555555555555555ul);
  	res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
  	res = (res + (res >> 4)) & 0x0F0F0F0F0F0F0F0Ful;
  	res = res + (res >> 8);
  	res = res + (res >> 16);
  	return (res + (res >> 32)) & 0x00000000000000FFul;
  #endif
  #endif
  }
  EXPORT_SYMBOL(__sw_hweight64);
  