C语言之测试程序运行时间

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int BitCount2(unsigned int n)
{

unsigned int c =0 ;
while(n!=0)
{

n &= (n -1) ; // 清除最低位的1
c++;
}
return c ;
}
int BitCount4(unsigned int n)
{
n = (n &0x55555555) + ((n >>1) &0x55555555) ;    //  n相邻位相加
n = (n &0x33333333) + ((n >>2) &0x33333333) ;    //  n（以2为单位）相邻位相加
n = (n &0x0f0f0f0f) + ((n >>4) &0x0f0f0f0f) ;    //  n（以4为单位）相邻位相加
n = (n &0x00ff00ff) + ((n >>8) &0x00ff00ff) ;    //  n（以8为单位）相邻位相加
n = (n &0x0000ffff) + ((n >>16) &0x0000ffff) ;   //  n（以16为单位）相邻位相加

return n ;
}
int  main( )
{
long i=100000000;
unsigned int n;
clock_t start, finish;
double Total_time;

start = clock();
while(--i)
n=BitCount2(123456789);
finish = clock();
printf( "bit number::%d \n", n);
Total_time = (double)(finish-start) / CLOCKS_PER_SEC;
printf( "BitCount2::%f seconds\n", Total_time);
printf( "\n", n);

i=100000000;
start = clock();
while(--i)
n=BitCount4(123456789);
finish = clock();
Total_time = (double)(finish-start) / CLOCKS_PER_SEC;
printf( "bit number::%d \n", n);
printf( "BitCount4::%f seconds\n", Total_time);

return 0;
}