CODEWITHSUNDEEP
javac++c
john
john

Reputation: 99

Generating Random number of 2^30

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?

Upvotes: 5

Views: 405

Answers (6)

kallikak
kallikak

Reputation: 842

Here's an old Usenet post with a number of interesting RNGs - all very easily implemented.

http://www.cse.yorku.ca/~oz/marsaglia-rng.html

They may not quite match the Mersenne twister, but I have made good use of several of them and they are certainly superior to some of the default rand() implementations. They pass the DIEHARD tests of randomness and the largest period generator included has period > 2^7700 and takes no more than a couple of lines to implement.

Upvotes: 1

bames53
bames53

Reputation: 88225

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.

Upvotes: 3

yeyo
yeyo

Reputation: 3009

g_random_int() return a random guint32 equally distributed over the range [0..2^32-1]. 

#include <glib.h>

int
main(void)
{
     g_print("%d\n", g_random_int());
   return 0;
}

with gcc:

gcc -o rand rand.c `pkg-config --cflags --libs glib-2.0`

EDIT:

reading directly from /dev/random (less portable), compile as usual:

#include <stdio.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>

int
main(void)
{
    int             fd;
    unsigned int    number;

    fd = open("/dev/random", O_RDONLY);

    read(fd, &number, sizeof(number));

    printf("%u\n", number);
    close(fd);
  return 0;
}

PS: check for errors.

Upvotes: 1

leonbloy
leonbloy

Reputation: 76016

A simple way to increment the randomness and period:

public class Random2 {

    private static int LEN = 64;
    private final int[] buf = new int[LEN];
    private Random r;
    private final int maxInt = 1 << 10;

    public Random2() {
        r = new Random();
        for (int i = 0; i < LEN; i++)
            buf[i] = r.nextInt(maxInt);
    }

    public int nextInt() {
        int i = r.nextInt(LEN);
        int x = buf[i];
        buf[i] = r.nextInt(maxInt);
        return x;
    }

}

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533870

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);

}

Upvotes: 2

Doug Currie
Doug Currie

Reputation: 41220

Mark A. Overton had a nice article on fairly simple but high quality RNGs on Dr. Dobbs on May 24, 2011

Upvotes: 0

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