DotyHumphreySmallFastCounting64.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.
- */
- package org.apache.commons.rng.core.source64;
- import org.apache.commons.rng.core.util.NumberFactory;
- /**
- * Implement the Small, Fast, Counting (SFC) 64-bit generator of Chris Doty-Humphrey.
- * The original source is the PractRand test suite by the same author.
- *
- * <p>The state size is 256-bits; the period is a minimum of 2<sup>64</sup> and an
- * average of approximately 2<sup>255</sup>.</p>
- *
- * @see <a href="http://pracrand.sourceforge.net/">PractRand</a>
- * @since 1.3
- */
- public class DotyHumphreySmallFastCounting64 extends LongProvider {
- /** Size of the seed. */
- private static final int SEED_SIZE = 3;
- /** State a. */
- private long a;
- /** State b. */
- private long b;
- /** State c. */
- private long c;
- /** Counter. */
- private long counter;
- /**
- * Creates an instance with the given seed.
- *
- * @param seed Initial seed.
- * If the length is larger than 3, only the first 3 elements will
- * be used; if smaller, the remaining elements will be automatically set.
- */
- public DotyHumphreySmallFastCounting64(long[] seed) {
- if (seed.length < SEED_SIZE) {
- final long[] state = new long[SEED_SIZE];
- fillState(state, seed);
- setSeedInternal(state);
- } else {
- setSeedInternal(seed);
- }
- }
- /**
- * Seeds the RNG.
- *
- * @param seed Seed.
- */
- private void setSeedInternal(long[] seed) {
- a = seed[0];
- b = seed[1];
- c = seed[2];
- counter = 1L;
- for (int i = 0; i < 18; i++) {
- next();
- }
- }
- /** {@inheritDoc} */
- @Override
- public final long next() {
- final long tmp = a + b + counter++;
- a = b ^ (b >>> 11);
- b = c + (c << 3);
- c = Long.rotateLeft(c, 24) + tmp;
- return tmp;
- }
- /** {@inheritDoc} */
- @Override
- protected byte[] getStateInternal() {
- return composeStateInternal(NumberFactory.makeByteArray(new long[] {a, b, c, counter}),
- super.getStateInternal());
- }
- /** {@inheritDoc} */
- @Override
- protected void setStateInternal(byte[] s) {
- final byte[][] parts = splitStateInternal(s, 4 * 8);
- final long[] tmp = NumberFactory.makeLongArray(parts[0]);
- a = tmp[0];
- b = tmp[1];
- c = tmp[2];
- counter = tmp[3];
- super.setStateInternal(parts[1]);
- }
- }