Generate uniform random numbers in [a, b] from 0/1 random number generator

gen_rand.cc

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
// Generate random numbers in large ranges with random number
// generator in small ranges

// For random number generator with 0/1, we can use it to generate bits
unsigned char zero_one()
{
    return rand() & 1;
}

unsigned gen_rand(unsigned a, unsigned b)
{
    if (a > b)
        return gen_rand(b, a);
    unsigned t = b - a;
    unsigned res = 0;
    do
    {
        res = 0;
        for (int ii = 0; (1u << ii) <= t; ++ii) {
            res <<= 1;
            res |= zero_one();
        }
    } while (res > t); // if outside the range, retry

    return res + a;
}

int main()
{
    srand(time(0));
    cout << "Generate " << 100 << " rand numbers" << endl;
    for (int ii = 0; ii < 100; ++ii)
        cout << gen_rand(0, 7) << endl;
    return 0;
}