How to calculate nearest bigger integer divisible by 8 in C++ bitwise operation?

Question

I need to calculate the nearest bigger integer devisible by 8. For examples:

1. for a=0, the nearest bigger integer devisible by 8 is 0.
2. for from a=1 to a=7, the nearest bigger integer devisible by 8 is 8.
3. for a=8, the nearest bigger integer devisible by 8 is 8.
4. for from a=x*8+1 to a=x*8+7, the nearest bigger integer devisible by 8 is a=(x+1)*8.
5. for a=x*8, the nearest bigger integer devisible by 8 is a=x*8 itself.

How should I implement this function int nearestBiggerIntegerDevisibleBy8(int a) in C++ bitwise operation (fastest)?

Answer 1

This one way to go about it

#include <stdio.h>

int nearestBiggerInt(int n){ 
    n += 7;
    return (n & ~7);
}

int main()
{
    for (int i = 0; i < 20; i++)
        printf("%d -> %d\n", i, nearestBiggerInt(i));
    return 0;
}

Output

0 -> 0
1 -> 8
2 -> 8
3 -> 8
4 -> 8
5 -> 8
6 -> 8
7 -> 8
8 -> 8
9 -> 16
10 -> 16
11 -> 16
12 -> 16
13 -> 16
14 -> 16
15 -> 16
16 -> 16
17 -> 24
18 -> 24
19 -> 24