MRG32k3a Combined recursive generator (pseudo-code)

   /* Constants */
   /* First generator */
   a1 = [0, 1403580, -810728]
   m1 = 2**32 - 209
   /* Second Generator */
   a2 = [527612, 0, -1370589]
   m2 = 2**32 - 22853
    
   d = m1 + 1
   
   class MRG32k3a
       x1 = [0, 0, 0]  /* list of three last values of gen #1 */
       x2 = [0, 0, 0]  /* list of three last values of gen #2 */
       
       method seed(u64 seed_state)
           assert seed_state in range >0 and < d 
           x1 = [seed_state, 0, 0]
           x2 = [seed_state, 0, 0]
       end method
           
       method next_int()
           x1i = (a1[0]*x1[0] + a1[1]*x1[1] + a1[2]*x1[2]) mod m1
           x2i = (a2[0]*x2[0] + a2[1]*x2[1] + a2[2]*x2[2]) mod m2
           x1 = [x1i, x1[0], x1[1]]    /* Keep last three */
           x2 = [x2i, x2[0], x2[1]]    /* Keep last three */
           z = (x1i - x2i) % m1
           answer = (z + 1)
           
           return answer
       end method
       
       method next_float():
           return float next_int() / d
       end method
       
   end class


MRG32k3a Use:
   random_gen = instance MRG32k3a
   random_gen.seed(1234567)
   print(random_gen.next_int())   /* 1459213977 */
   print(random_gen.next_int())   /* 2827710106 */
   print(random_gen.next_int())   /* 4245671317 */
   print(random_gen.next_int())   /* 3877608661 */
   print(random_gen.next_int())   /* 2595287583 */
   
       

Task
 Generate a class/set of functions that generates pseudo-random
numbers as shown above.

 Show that the first five integers generated with the seed `1234567`
are as shown above

 Show that for an initial seed of '987654321' the counts of 100_000
repetitions of

   floor(random_gen.next_float() * 5)

Is as follows:

   0: 20002, 1: 20060, 2: 19948, 3: 20059, 4: 19931

 Show your output here, on this page.


public class App {
    private static long mod(long x, long y) {
        long m = x % y;
        if (m < 0) {
            if (y < 0) {
                return m - y;
            } else {
                return m + y;
            }
        }
        return m;
    }
 
    public static class RNG {
        // first generator
        private final long[] a1 = {0, 1403580, -810728};
        private static final long m1 = (1L << 32) - 209;
        private long[] x1;
        // second generator
        private final long[] a2 = {527612, 0, -1370589};
        private static final long m2 = (1L << 32) - 22853;
        private long[] x2;
        // other
        private static final long d = m1 + 1;
 
        public void seed(long state) {
            x1 = new long[]{state, 0, 0};
            x2 = new long[]{state, 0, 0};
        }
 
        public long nextInt() {
            long x1i = mod(a1[0] * x1[0] + a1[1] * x1[1] + a1[2] * x1[2], m1);
            long x2i = mod(a2[0] * x2[0] + a2[1] * x2[1] + a2[2] * x2[2], m2);
            long z = mod(x1i - x2i, m1);
 
            // keep the last three values of the first generator
            x1 = new long[]{x1i, x1[0], x1[1]};
            // keep the last three values of the second generator
            x2 = new long[]{x2i, x2[0], x2[1]};
 
            return z + 1;
        }
 
        public double nextFloat() {
            return 1.0 * nextInt() / d;
        }
    }
 
    public static void main(String[] args) {
        RNG rng = new RNG();
 
        rng.seed(1234567);
        System.out.println(rng.nextInt());
        System.out.println(rng.nextInt());
        System.out.println(rng.nextInt());
        System.out.println(rng.nextInt());
        System.out.println(rng.nextInt());
        System.out.println();
 
        int[] counts = {0, 0, 0, 0, 0};
        rng.seed(987654321);
        for (int i = 0; i < 100_000; i++) {
            int value = (int) Math.floor(rng.nextFloat() * 5.0);
            counts[value]++;
        }
        for (int i = 0; i < counts.length; i++) {
            System.out.printf("%d: %d%n", i, counts[i]);
        }
    }
}