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Commons Math example source code file (BitsStreamGenerator.java)

This example Commons Math source code file (BitsStreamGenerator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Math tags/keywords

bitsstreamgenerator, bitsstreamgenerator, illegalargumentexception, illegalargumentexception, randomgenerator, randomgenerator

The Commons Math BitsStreamGenerator.java source code

/*
 * 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.math.random;

import org.apache.commons.math.MathRuntimeException;

/** Base class for random number generators that generates bits streams.

 * @version $Revision: 811685 $ $Date: 2009-09-05 13:36:48 -0400 (Sat, 05 Sep 2009) $
 * @since 2.0

 */
public abstract class BitsStreamGenerator implements RandomGenerator {

    /** 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 void nextBytes(byte[] bytes) {
        int i = 0;
        final int iEnd = bytes.length - 3;
        while (i < iEnd) {
            final int random = next(32);
            bytes[i]     = (byte) (random & 0xff);
            bytes[i + 1] = (byte) ((random >>  8) & 0xff);
            bytes[i + 2] = (byte) ((random >> 16) & 0xff);
            bytes[i + 3] = (byte) ((random >> 24) & 0xff);
            i += 4;
        }
        int random = next(32);
        while (i < bytes.length) {
            bytes[i++] = (byte) (random & 0xff);
            random     = random >> 8;
        }
    }

    /** {@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 * Math.PI * x;
            final double r      = Math.sqrt(-2 * Math.log(y));
            random       = r * Math.cos(alpha);
            nextGaussian = r * Math.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} */
    public int nextInt(int n) throws IllegalArgumentException {

        if (n < 1) {
            throw MathRuntimeException.createIllegalArgumentException(
                  "upper bound must be positive ({0})", n);
        }

        // find bit mask for n
        int mask = n;
        mask |= mask >> 1;
        mask |= mask >> 2;
        mask |= mask >> 4;
        mask |= mask >> 8;
        mask |= mask >> 16;

        while (true) {
            final int random = next(32) & mask;
            if (random < n) {
                return random;
            }
        }

    }

    /** {@inheritDoc} */
    public long nextLong() {
        final long high  = ((long) next(32)) << 32;
        final long  low  = ((long) next(32)) & 0xffffffffL;
        return high | low;
    }

}

Other Commons Math examples (source code examples)

Here is a short list of links related to this Commons Math BitsStreamGenerator.java source code file:

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