R250_521.java

/**
 * Placed in public domain
 * http://www.qbrundage.com/michaelb/pubs/essays/random_number_generation.html
 */

package org.apache.hadoop.hashtable;

/**
 * Random number generator.
 *
 * @author tomasz
 *
 */
public final class R250_521 {
  private int r250_index;
  private int r521_index;
  private int[] r250_buffer = new int[250];
  private int[] r521_buffer = new int[521];

  public R250_521() {
    java.util.Random r = new java.util.Random();
    int i = 521;
    int mask1 = 1;
    int mask2 = 0xFFFFFFFF;

    while (i-- > 250) {
      r521_buffer[i] = r.nextInt();
    }
    while (i-- > 31) {
      r250_buffer[i] = r.nextInt();
      r521_buffer[i] = r.nextInt();
    }

    while (i-- > 0) {
      r250_buffer[i] = (r.nextInt() | mask1) & mask2;
      r521_buffer[i] = (r.nextInt() | mask1) & mask2;
      mask2 ^= mask1;
      mask1 >>= 1;
    }
    r250_buffer[0] = mask1;
    r521_buffer[0] = mask2;
    r250_index = 0;
    r521_index = 0;
  }

  public int random() {
    int i1 = r250_index;
    int i2 = r521_index;

    int j1 = i1 - (250 - 103);
    if (j1 < 0)
      j1 = i1 + 103;
    int j2 = i2 - (521 - 168);
    if (j2 < 0)
      j2 = i2 + 168;

    int r = r250_buffer[j1] ^ r250_buffer[i1];
    r250_buffer[i1] = r;
    int s = r521_buffer[j2] ^ r521_buffer[i2];
    r521_buffer[i2] = s;

    i1 = (i1 != 249) ? (i1 + 1) : 0;
    r250_index = i1;
    i2 = (i2 != 520) ? (i2 + 1) : 0;
    r521_index = i2;

    return r ^ s;
  }
}