math.rng.DefaultRng Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of finwhale Show documentation
Statistical distributions library (in statu nascendi)
The newest version!
/*
 * Copyright 2013 SPZ
 *
 * Licensed 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.
 */
package math.rng;

public final class DefaultRng {

    public static PseudoRandom getGlobalPseudoRandom() {
        return MersenneTwister64.getDefault();
    }

    public static PseudoRandom newPseudoRandom() {
        return new MersenneTwister64();
    }

    public static PseudoRandom newPseudoRandom(final long seed) {
        return new MersenneTwister64(seed);
    }

    public static PseudoRandom newPseudoRandom(final long[] seed) {
        return new MersenneTwister64(seed);
    }

    public static PseudoRandom[] newIndepPseudoRandoms(final int count) {
        if (count <= 0) {
            throw new IllegalArgumentException("count <= 0 : " + count);
        }
        if (count == 1) {
            return new PseudoRandom[] { newPseudoRandom() };
        }
        final int NN = 312;
        final long[] seed = new long[NN];
        getGlobalPseudoRandom().nextLongs(seed);
        final PseudoRandom[] multiplePrng = new PseudoRandom[count];
        for (int i = 0; i < multiplePrng.length; ++i) {
            final PseudoRandom prng = newPseudoRandom(seed);
            // now change the seed
            reseed(NN, seed, prng);
            multiplePrng[i] = prng;
        }
        return multiplePrng;
    }

    public static PseudoRandom newIndepPseudoRandom(
            final PseudoRandom prng) {
        final int NN = 312;
        final long[] seed = new long[NN];
        reseed(NN, seed, prng);
        return newPseudoRandom(seed);
    }

    private static void reseed(final int len, final long[] seed,
            final PseudoRandom prng) {
        prng.nextLongs(seed);
        int j = 0;
        while (j < seed.length && seed[j] == 0L) {
            ++j;
        }
        final long nucleus = (j < seed.length) ? seed[j] : -1L;
        final long[] half_seed = new long[len / 2];
        new MarsagliaXOR64(nucleus ^ Seed.seed()).nextLongs(half_seed);
        System.arraycopy(half_seed, 0, seed, 0, half_seed.length);
    }

    private DefaultRng() {
        throw new AssertionError();
    }
}