unsigned int concat

// Based on http://stackoverflow.com/a/25934909

static unsigned int const pow10[] = {
    1,
    10,
    100,
    1000,
    10000,
    100000,
    1000000,
    10000000,
    100000000,
    1000000000,
};

unsigned int base2digits(unsigned int x) {
    return x ? 32 - __builtin_clz(x) : 0;
}

unsigned int base10digits(unsigned int x) {
    static unsigned int const guess[33] = {
        0, 0, 0, 0, 1, 1, 1, 2, 2, 2,
        3, 3, 3, 3, 4, 4, 4, 5, 5, 5,
        6, 6, 6, 6, 7, 7, 7, 8, 8, 8,
        9, 9, 9
    };
    unsigned int digits = guess[base2digits(x)];
    return digits + (x >= pow10[digits]);
}

unsigned int concat(unsigned int a, unsigned int b) {
    return a * pow10[base10digits(b)] + b;
}