cmathbit-manipulationdivisiondivide

Divide a number by 3 without using *, /, +, -, % operators


How would you divide a number by 3 without using *, /, +, -, %, operators?

The number may be signed or unsigned.


Solution

  • This is a simple function which performs the desired operation. But it requires the + operator, so all you have left to do is to add the values with bit-operators:

    // replaces the + operator
    int add(int x, int y)
    {
        while (x) {
            int t = (x & y) << 1;
            y ^= x;
            x = t;
        }
        return y;
    }
    
    int divideby3(int num)
    {
        int sum = 0;
        while (num > 3) {
            sum = add(num >> 2, sum);
            num = add(num >> 2, num & 3);
        }
        if (num == 3)
            sum = add(sum, 1);
        return sum; 
    }
    

    As Jim commented this works, because: