Ex_2.9_bitcount2s.c

/* In twos complement number systems, x &= (x-1) deletes the rightmost 1 bit in x.
 * Explain why? Use this to right a faster version of bitcount. Bitcount program counts
 * the number of 1 bits in the integer */

#include<stdio.h>

int bitcount(unsigned x);

int main(void)
{
	printf("%d",bitcount((unsigned)12));
}

int bitcount(unsigned x)
{
	int b;

	for(b=0; x!=0; x &= x-1)
		++b;

	return b;
}