Generating Random number of 2^30

Question

I want to generate 2^30 random numbers in the range of 0 to 2^10. I heard that rand() function is not suitable for this many numbers.Is there any another way to generate it with nearly equal distribution?

Answer 1

The C++ <random> library is an excellent option, with many choices of PRNG engine and distribution.

#include <random>
#include <cstdint>
#include <iostream>

int main() {
    std::random_device r;
    std::seed_seq seed{r(), r(), r(), r(), r(), r(), r(), r()};
    std::mt19937_64 eng(seed);
    std::uniform_int_distribution<> dist(0, 1<<10);

    for (std::uint32_t i = 0; i< (1<<30); ++i) {
        int value = dist(eng);
        std::cout << value << ' ';
    }
}

Also, random_device is itself an engine which may, depending on the implementation, provide access to a non-deterministic or cryptographic RNG:

std::random_device eng;
std::cout << dist(eng) << '\n';

For example in libc++ it uses /dev/urandom by default, which on OS X uses the Yarrow cryptographic RNG algorithm.

Answer 2

In Java you can use Random which does repeat after 2^48 values.

Random rand = new Random();

for(int i = 0; i < (1<<30); i++) {
    int n = rand.nextInt(1 << 10);

}