K&R C Exercise 2-9 Solution

/* * Exercise 2-9 In a two's complement number system,  * x & ( x - 1 ) deletes the rightmost 1-bit in x. * Use this to write a fast version of bitcount. *  * Written by fduan on Dec. 14, 2011. */#include <stdio.h>/* count the number of 1 bits in x */int bit_count( unsigned x ){int n;for( n = 0; x != 0; x >>= 1 )if( x & 01 != 0 )++n;return n;}/* fast version of bit_count */int fast_bit_count( unsigned x ){int n = 0;while( x != 0 ){x &= ( x - 1 );++n;}return n;}int main(){unsigned x = 100;printf( "%u, %u\n", bit_count( x ), fast_bit_count( x ) );return 0;}