001 /*
002 * Java Genetic Algorithm Library (jenetics-7.1.1).
003 * Copyright (c) 2007-2022 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 * Author:
018 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020 package io.jenetics.ext.internal.util;
021
022 import static java.lang.String.format;
023
024 import java.math.BigInteger;
025 import java.util.random.RandomGenerator;
026
027 import io.jenetics.util.RandomAdapter;
028
029 /**
030 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
031 * @version 3.5
032 * @since 3.5
033 */
034 public class Randoms {
035 private Randoms() {}
036
037 /**
038 * Returns a pseudo-random, uniformly distributed int value between 0
039 * (inclusive) and the specified value (exclusive), drawn from the given
040 * random number generator's sequence.
041 *
042 * @param n the bound on the random number to be returned. Must be
043 * positive.
044 * @param random the random engine used for creating the random number.
045 * @return the next pseudo-random, uniformly distributed int value
046 * between 0 (inclusive) and n (exclusive) from the given random
047 * number generator's sequence
048 * @throws IllegalArgumentException if n is smaller than 1.
049 * @throws NullPointerException if the given {@code random}
050 * engine of the maximal value {@code n} is {@code null}.
051 */
052 public static BigInteger nextBigInteger(
053 final BigInteger n,
054 final RandomGenerator random
055 ) {
056 if (n.compareTo(BigInteger.ONE) < 0) {
057 throw new IllegalArgumentException(format(
058 "n is smaller than one: %d", n
059 ));
060 }
061
062 BigInteger result = null;
063 if (n.bitLength() <= Integer.SIZE - 1) {
064 result = BigInteger.valueOf(random.nextInt(n.intValue()));
065 } else if (n.bitLength() <= Long.SIZE - 1) {
066 result = BigInteger.valueOf(random.nextLong(n.longValue()));
067 } else {
068 final var rnd = RandomAdapter.of(random);
069 do {
070 result = new BigInteger(n.bitLength(), rnd).mod(n);
071 } while (result.compareTo(n) > 0);
072 }
073
074 return result;
075 }
076
077 /**
078 * Returns a pseudo-random, uniformly distributed int value between min
079 * and max (min and max included).
080 *
081 * @param min lower bound for generated long integer (inclusively)
082 * @param max upper bound for generated long integer (exclusively)
083 * @param random the random engine to use for calculating the random
084 * long value
085 * @return a random long integer greater than or equal to {@code min}
086 * and less than or equal to {@code max}
087 * @throws IllegalArgumentException if {@code min >= max}
088 * @throws NullPointerException if one of the given parameters
089 * are {@code null}.
090 */
091 public static BigInteger nextBigInteger(
092 final BigInteger min,
093 final BigInteger max,
094 final RandomGenerator random
095 ) {
096 if (min.compareTo(max) > 0) {
097 throw new IllegalArgumentException(format(
098 "min >= max: %d > %d.", min, max
099 ));
100 }
101
102 final BigInteger n = max.subtract(min);
103 return nextBigInteger(n, random).add(min);
104 }
105
106 }
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