| /* |
| * 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.math3.random; |
| |
| import java.io.Serializable; |
| |
| import org.apache.commons.math3.exception.NotStrictlyPositiveException; |
| import org.apache.commons.math3.exception.OutOfRangeException; |
| import org.apache.commons.math3.util.FastMath; |
| |
| /** Base class for random number generators that generates bits streams. |
| * |
| * @since 2.0 |
| */ |
| public abstract class BitsStreamGenerator |
| implements RandomGenerator, |
| Serializable { |
| /** Serializable version identifier */ |
| private static final long serialVersionUID = 20130104L; |
| /** Next gaussian. */ |
| private double nextGaussian; |
| |
| /** |
| * Creates a new random number generator. |
| */ |
| public BitsStreamGenerator() { |
| nextGaussian = Double.NaN; |
| } |
| |
| /** {@inheritDoc} */ |
| public abstract void setSeed(int seed); |
| |
| /** {@inheritDoc} */ |
| public abstract void setSeed(int[] seed); |
| |
| /** {@inheritDoc} */ |
| public abstract void setSeed(long seed); |
| |
| /** Generate next pseudorandom number. |
| * <p>This method is the core generation algorithm. It is used by all the |
| * public generation methods for the various primitive types {@link |
| * #nextBoolean()}, {@link #nextBytes(byte[])}, {@link #nextDouble()}, |
| * {@link #nextFloat()}, {@link #nextGaussian()}, {@link #nextInt()}, |
| * {@link #next(int)} and {@link #nextLong()}.</p> |
| * @param bits number of random bits to produce |
| * @return random bits generated |
| */ |
| protected abstract int next(int bits); |
| |
| /** {@inheritDoc} */ |
| public boolean nextBoolean() { |
| return next(1) != 0; |
| } |
| |
| /** {@inheritDoc} */ |
| public double nextDouble() { |
| final long high = ((long) next(26)) << 26; |
| final int low = next(26); |
| return (high | low) * 0x1.0p-52d; |
| } |
| |
| /** {@inheritDoc} */ |
| public float nextFloat() { |
| return next(23) * 0x1.0p-23f; |
| } |
| |
| /** {@inheritDoc} */ |
| public double nextGaussian() { |
| |
| final double random; |
| if (Double.isNaN(nextGaussian)) { |
| // generate a new pair of gaussian numbers |
| final double x = nextDouble(); |
| final double y = nextDouble(); |
| final double alpha = 2 * FastMath.PI * x; |
| final double r = FastMath.sqrt(-2 * FastMath.log(y)); |
| random = r * FastMath.cos(alpha); |
| nextGaussian = r * FastMath.sin(alpha); |
| } else { |
| // use the second element of the pair already generated |
| random = nextGaussian; |
| nextGaussian = Double.NaN; |
| } |
| |
| return random; |
| |
| } |
| |
| /** {@inheritDoc} */ |
| public int nextInt() { |
| return next(32); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * <p>This default implementation is copied from Apache Harmony |
| * java.util.Random (r929253).</p> |
| * |
| * <p>Implementation notes: <ul> |
| * <li>If n is a power of 2, this method returns |
| * {@code (int) ((n * (long) next(31)) >> 31)}.</li> |
| * |
| * <li>If n is not a power of 2, what is returned is {@code next(31) % n} |
| * with {@code next(31)} values rejected (i.e. regenerated) until a |
| * value that is larger than the remainder of {@code Integer.MAX_VALUE / n} |
| * is generated. Rejection of this initial segment is necessary to ensure |
| * a uniform distribution.</li></ul></p> |
| */ |
| public int nextInt(int n) throws IllegalArgumentException { |
| if (n > 0) { |
| if ((n & -n) == n) { |
| return (int) ((n * (long) next(31)) >> 31); |
| } |
| int bits; |
| int val; |
| do { |
| bits = next(31); |
| val = bits % n; |
| } while (bits - val + (n - 1) < 0); |
| return val; |
| } |
| throw new NotStrictlyPositiveException(n); |
| } |
| |
| /** {@inheritDoc} */ |
| public long nextLong() { |
| final long high = ((long) next(32)) << 32; |
| final long low = ((long) next(32)) & 0xffffffffL; |
| return high | low; |
| } |
| |
| /** |
| * Returns a pseudorandom, uniformly distributed {@code long} value |
| * between 0 (inclusive) and the specified value (exclusive), drawn from |
| * this random number generator's sequence. |
| * |
| * @param n the bound on the random number to be returned. Must be |
| * positive. |
| * @return a pseudorandom, uniformly distributed {@code long} |
| * value between 0 (inclusive) and n (exclusive). |
| * @throws IllegalArgumentException if n is not positive. |
| */ |
| public long nextLong(long n) throws IllegalArgumentException { |
| if (n > 0) { |
| long bits; |
| long val; |
| do { |
| bits = ((long) next(31)) << 32; |
| bits |= ((long) next(32)) & 0xffffffffL; |
| val = bits % n; |
| } while (bits - val + (n - 1) < 0); |
| return val; |
| } |
| throw new NotStrictlyPositiveException(n); |
| } |
| |
| /** |
| * Clears the cache used by the default implementation of |
| * {@link #nextGaussian}. |
| */ |
| public void clear() { |
| nextGaussian = Double.NaN; |
| } |
| |
| /** |
| * Generates random bytes and places them into a user-supplied array. |
| * |
| * <p> |
| * The array is filled with bytes extracted from random integers. |
| * This implies that the number of random bytes generated may be larger than |
| * the length of the byte array. |
| * </p> |
| * |
| * @param bytes Array in which to put the generated bytes. Cannot be {@code null}. |
| */ |
| @Override |
| public void nextBytes(byte[] bytes) { |
| nextBytesFill(bytes, 0, bytes.length); |
| } |
| |
| /** |
| * Generates random bytes and places them into a user-supplied array. |
| * |
| * <p> |
| * The array is filled with bytes extracted from random integers. |
| * This implies that the number of random bytes generated may be larger than |
| * the length of the byte array. |
| * </p> |
| * |
| * @param bytes Array in which to put the generated bytes. Cannot be {@code null}. |
| * @param start Index at which to start inserting the generated bytes. |
| * @param len Number of bytes to insert. |
| * @throws OutOfRangeException if {@code start < 0} or {@code start >= bytes.length}. |
| * @throws OutOfRangeException if {@code len < 0} or {@code len > bytes.length - start}. |
| */ |
| public void nextBytes(byte[] bytes, |
| int start, |
| int len) { |
| if (start < 0 || |
| start >= bytes.length) { |
| throw new OutOfRangeException(start, 0, bytes.length); |
| } |
| if (len < 0 || |
| len > bytes.length - start) { |
| throw new OutOfRangeException(len, 0, bytes.length - start); |
| } |
| |
| nextBytesFill(bytes, start, len); |
| } |
| |
| /** |
| * Generates random bytes and places them into a user-supplied array. |
| * |
| * <p> |
| * The array is filled with bytes extracted from random integers. |
| * This implies that the number of random bytes generated may be larger than |
| * the length of the byte array. |
| * </p> |
| * |
| * @param bytes Array in which to put the generated bytes. Cannot be {@code null}. |
| * @param start Index at which to start inserting the generated bytes. |
| * @param len Number of bytes to insert. |
| */ |
| private void nextBytesFill(byte[] bytes, |
| int start, |
| int len) { |
| int index = start; // Index of first insertion. |
| |
| // Index of first insertion plus multiple 4 part of length (i.e. length |
| // with two least significant bits unset). |
| final int indexLoopLimit = index + (len & 0x7ffffffc); |
| |
| // Start filling in the byte array, 4 bytes at a time. |
| while (index < indexLoopLimit) { |
| final int random = next(32); |
| bytes[index++] = (byte) random; |
| bytes[index++] = (byte) (random >>> 8); |
| bytes[index++] = (byte) (random >>> 16); |
| bytes[index++] = (byte) (random >>> 24); |
| } |
| |
| final int indexLimit = start + len; // Index of last insertion + 1. |
| |
| // Fill in the remaining bytes. |
| if (index < indexLimit) { |
| int random = next(32); |
| while (true) { |
| bytes[index++] = (byte) random; |
| if (index < indexLimit) { |
| random >>>= 8; |
| } else { |
| break; |
| } |
| } |
| } |
| } |
| } |