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Linux/tools/perf/util/hweight.c

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  1 #include <linux/bitops.h>
  2 
  3 /**
  4  * hweightN - returns the hamming weight of a N-bit word
  5  * @x: the word to weigh
  6  *
  7  * The Hamming Weight of a number is the total number of bits set in it.
  8  */
  9 
 10 unsigned int hweight32(unsigned int w)
 11 {
 12         unsigned int res = w - ((w >> 1) & 0x55555555);
 13         res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
 14         res = (res + (res >> 4)) & 0x0F0F0F0F;
 15         res = res + (res >> 8);
 16         return (res + (res >> 16)) & 0x000000FF;
 17 }
 18 
 19 unsigned long hweight64(__u64 w)
 20 {
 21 #if BITS_PER_LONG == 32
 22         return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w);
 23 #elif BITS_PER_LONG == 64
 24         __u64 res = w - ((w >> 1) & 0x5555555555555555ul);
 25         res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
 26         res = (res + (res >> 4)) & 0x0F0F0F0F0F0F0F0Ful;
 27         res = res + (res >> 8);
 28         res = res + (res >> 16);
 29         return (res + (res >> 32)) & 0x00000000000000FFul;
 30 #endif
 31 }
 32 

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