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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.rng.simple.internal;
18  
19  import org.apache.commons.rng.core.source64.SplitMix64;
20  import org.apache.commons.rng.core.util.NumberFactory;
21  
22  /**
23   * Uses a {@code long} value to seed a {@link SplitMix64} RNG and
24   * create a {@code int[]} with the requested number of random
25   * values.
26   *
27   * @since 1.0
28   */
29  public class Long2IntArray implements Seed2ArrayConverter<Long, int[]> {
30      /** Size of the output array. */
31      private final int size;
32  
33      /**
34       * @param size Size of the output array.
35       */
36      public Long2IntArray(int size) {
37          this.size = size;
38      }
39  
40      /** {@inheritDoc} */
41      @Override
42      public int[] convert(Long seed) {
43          return convertSeed(seed, size);
44      }
45  
46      /**
47       * {@inheritDoc}
48       *
49       * @since 1.3
50       */
51      @Override
52      public int[] convert(Long seed, int outputSize) {
53          return convertSeed(seed, outputSize);
54      }
55  
56      /**
57       * Convert the seed.
58       *
59       * @param seed Input seed.
60       * @param size Output array size.
61       * @return the converted seed.
62       */
63      private static int[] convertSeed(Long seed, int size) {
64          final int[] out = new int[size];
65          final SplitMix64 rng = new SplitMix64(seed);
66          // Fill pairs of ints from a long.
67          // The array is filled from the end towards the start.
68          for (int i = size - 1; i > 0; i -= 2) {
69              final long v = rng.nextLong();
70              out[i] = NumberFactory.extractHi(v);
71              out[i - 1] = NumberFactory.extractLo(v);
72          }
73          // An odd size requires a final single int at the start
74          if ((size & 1) == 1) {
75              out[0] = NumberFactory.extractHi(rng.nextLong());
76          }
77          return out;
78      }
79  }