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.

There is a simple function I found here. but it's using the + operator, so you have to add the values with the bit-operators:

// replaces the + operator
int add(int x, int y) {
    int a, b;
    do {
        a = x & y;
        b = x ^ y;
        x = a << 1;
        y = b;
    } while (a);
    return b;
}
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; }