commons-rng-core/src/test/java/org/apache/commons/rng/core/source64/TwoCmresTest.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
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package org.apache.commons.rng.core.source64;

import org.apache.commons.rng.core.RandomAssert;
import org.apache.commons.rng.core.source64.TwoCmres.Cmres;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import java.util.ArrayList;


class TwoCmresTest {
    @Test
    void testAsymmetric() {
        final int index1 = 2;
        final int index2 = 5;
        final int seed = -123456789;

        final TwoCmres rng1 = new TwoCmres(seed, index1, index2);
        final TwoCmres rng2 = new TwoCmres(seed, index2, index1);

        // Try a few values.
        final int n = 1000;
        for (int[] i = {0}; i[0] < n; i[0]++) {
            Assertions.assertNotEquals(rng1.nextLong(), rng2.nextLong(), () -> "i=" + i[0]);
        }
    }

    /**
     * This test targets the seeding procedure to verify any bit of the input seed contributes
     * to the output. Note: The seeding routine creates 2 16-bit integers from the 32-bit seed,
     * thus a change of any single bit should make a different output.
     */
    @Test
    void testSeedingWithASingleBitProducesDifferentOutputFromZeroSeed() {
        final int n = 100;

        // Output with a zero seed
        final long[] values = new long[n];
        final TwoCmres rng = new TwoCmres(0);
        for (int i = 0; i < n; i++) {
            values[i] = rng.nextLong();
        }

        // Seed with a single bit
        for (int bit = 0; bit < 32; bit++) {
            final int seed = 1 << bit;
            RandomAssert.assertNotEquals(values, new TwoCmres(seed));
        }
    }

    @Test
    void testSubcycleGeneratorsMustBeDifferent() {
        final int max = TwoCmres.numberOfSubcycleGenerators();
        for (int i = 0; i < max; i++) {
            final int subCycle = i;
            Assertions.assertThrows(IllegalArgumentException.class,
                () -> new TwoCmres(-97845, subCycle, subCycle));
        }
    }

    @Test
    void testSubcycleGeneratorsIndex() {
        final int seed = 246810;

        // Valid indices are between 0 (included) and max (excluded).
        final int max = TwoCmres.numberOfSubcycleGenerators();

        for (int i = 0; i < max; i++) {
            for (int j = 0; j < max; j++) {
                if (i != j) { // Subcycle generators must be different.
                    // Can be instantiated.
                    new TwoCmres(seed, i, j);
                }
            }
        }

        for (int wrongIndex : new int[] {-1, max}) {
            Assertions.assertThrows(IndexOutOfBoundsException.class,
                () -> new TwoCmres(seed, wrongIndex, 1),
                () -> "Exception expected for index i = " + wrongIndex);
            Assertions.assertThrows(IndexOutOfBoundsException.class,
                () -> new TwoCmres(seed, 1, wrongIndex),
                () -> "Exception expected for index j = " + wrongIndex);
        }
    }

    @Test
    void testCmresFactoryThrowsWithDuplicateMultiplier() {
        final ArrayList<Cmres> list = new ArrayList<>();
        final long multiply = 0;
        final int rotate = 3;
        final int start = 5;

        list.add(new Cmres(multiply, rotate, start));

        long nextMultiply = multiply + 1;
        Assertions.assertDoesNotThrow(
            () -> Cmres.Factory.checkUnique(list, nextMultiply),
            () -> "The next multiply should be unique: " + nextMultiply);

        list.add(new Cmres(nextMultiply, rotate, start));
        // This should throw as the list now contains the multiply value
        Assertions.assertThrows(IllegalStateException.class, () -> Cmres.Factory.checkUnique(list, nextMultiply));
    }
}