Thread: Function purpose

Hi ,
Could you please help me understand what the "test" function do ?
test(15,8) >> gives 16
test(7,15) >> gives 17

thanks

Code:

#include <stdio.h>

int test(unsigned int n ,unsigned int m);

int main()
{

unsigned int k;

k=test(15,8);
printf("k= %d\n",k);  // k=16

return 0;
}

int test(unsigned int n ,unsigned int m)
{
return (n+m -1)& ~ (m-1);
}

If you want to understand bit operations, write down the binary representation of the values and do the operations on paper.

Bye, Andreas

Looks like m should be a power of 2. What the function does is round a number up and then mask off the lower bits. So if the call is test(x,8), then you get multples of 8: 0 == x returns 0, 0 < x <= 8 returns 8, 8 < x <= 16 returns 16. If the call is test(y,16), then 0 == y returns 0, 0 < y <= 16 returns 16, 16 < y <= 32 returns 32, ...