EN
Java - own random number generator (custom implementation)
14 points
In java we can implement custom random number generator by using LCG (Linear congruential generator) algorithm. LCG is one of the oldest and best-known pseudorandom number generator algorithm. We can adjust this implementation to work on int or long.
Linear congruential generator is defined by recurrence relation:
Where:
- Xn+1 - new seed
- a - MULTIPLIER_A
- Xn - current seed field
- c - INCREMENT_C
- m - MODULUS
In our below implementation above variables were used.
Note:
Every time
randomNumber()method is called, we assign new value to seed.
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/**2
* Based on long as int can overflow.3
*/4
public class RandomUtil {5
6
private final static long MULTIPLIER_A = 1103515245L;7
private final static long INCREMENT_C = 12345L;8
private final static long MODULUS = 2147483647L; // max int9
10
private static long seed = 3819201L;11
12
public static long randomNumber() {13
// we use long instead of int, as int can overflow 14
// when seed * MULTIPLIER_A + INCREMENT_C 15
seed = (seed * MULTIPLIER_A + INCREMENT_C) % MODULUS;16
return seed;17
}18
19
public static long randomPositiveNumber() {20
long tmp = randomNumber();21
if (tmp < 0) {22
seed = tmp * -1;23
}24
return seed;25
}26
27
public static void main(String[] args) {28
System.out.println(randomPositiveNumber()); // 180111810629
System.out.println(randomPositiveNumber()); // 4121118930
System.out.println(randomPositiveNumber()); // 1173857031
32
for (int i = 0; i < 7; i++) {33
System.out.println(randomPositiveNumber());34
}35
}36
}Output:
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18011181062
412111893
117385704
8652992595
8879589526
9926203517
17937530768
4772978919
162037936010
1194566247Below 2 fields:
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long MULTIPLIER_A = 1103515245L;2
long INCREMENT_C = 12345L;are used by runtime libraries of various compilers:
- glibc (used by GCC)
- ANSI C: Watcom, Digital Mars, CodeWarrior, IBM VisualAge C/C++
- C90, C99, C11: Suggestion in the ISO/IEC 9899, C18
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import java.util.Arrays;2
3
public class RandomUtilProbabilityTest {4
5
public static void main(String[] args) {6
int[] probabilityDistribution = new int[10];7
8
for (int i = 0; i < 30_000; i++) {9
long next = RandomUtil.randomPositiveNumber() % 10L;10
probabilityDistribution[(int) next]++;11
}12
13
// [2979, 3049, 3000, 2971, 2975, 2954, 3016, 3072, 3027, 2957]14
System.out.println(Arrays.toString(probabilityDistribution));15
16
// 3000017
System.out.println(Arrays.stream(probabilityDistribution).sum());18
19
int min = Integer.MAX_VALUE;20
int max = Integer.MIN_VALUE;21
22
for (int i = 0; i < probabilityDistribution.length; i++) {23
int next = probabilityDistribution[i];24
min = Math.min(min, next);25
max = Math.max(max, next);26
}27
28
System.out.println(" min: " + min); // min: 295429
System.out.println(" max: " + max); // max: 307230
System.out.println("diff: " + (max - min)); // diff: 11831
}32
}Output:
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[2979, 3049, 3000, 2971, 2975, 2954, 3016, 3072, 3027, 2957]2
300003
min: 29544
max: 30725
diff: 118xxxxxxxxxx1
import java.util.Arrays;2
import java.util.Random;3
4
public class JdkRandomProbabilityTest {5
6
private static final Random random = new Random(3819201);7
8
public static int nextInt(int min, int max) {9
return random.nextInt((max - min) + 1) + min;10
}11
12
public static void main(String[] args) {13
int[] probabilityDistribution = new int[10];14
15
for (int i = 0; i < 30_000; i++) {16
int next = nextInt(0, Integer.MAX_VALUE - 1) % 10;17
probabilityDistribution[next]++;18
}19
20
// [2963, 2885, 3049, 3041, 3002, 3089, 2967, 3020, 3019, 2965]21
System.out.println(Arrays.toString(probabilityDistribution));22
23
int min = Integer.MAX_VALUE;24
int max = Integer.MIN_VALUE;25
26
for (int i = 0; i < probabilityDistribution.length; i++) {27
int next = probabilityDistribution[i];28
min = Math.min(min, next);29
max = Math.max(max, next);30
}31
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System.out.println(" min: " + min); // min: 290333
System.out.println(" max: " + max); // max: 309334
System.out.println("diff: " + (max - min)); // diff: 19035
}36
}Output:
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[2976, 2984, 3091, 3093, 3037, 2969, 3030, 2903, 2905, 3012]2
min: 29033
max: 30934
diff: 190