/*
* 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 java.util;
import java.io.Serializable;
/**
* This class provides methods that generates pseudo-random numbers of different
* types, such as {@code int}, {@code long}, {@code double}, and {@code float}.
*
* @see Properties
* @see PropertyResourceBundle
* @since Android 1.0
*/
public class Random implements Serializable {
private static final long serialVersionUID = 3905348978240129619L;
static final long multiplier = 0x5deece66dL;
/**
* The boolean value indicating if the second Gaussian number is available.
*
* @serial
*/
boolean haveNextNextGaussian = false;
/**
* It is associated with the internal state of this generator.
*
* @serial
*/
long seed;
/**
* The second Gaussian generated number.
*
* @serial
*/
double nextNextGaussian = 0;
/**
* Construct a random generator with the current time of day in milliseconds
* as the initial state.
*
* @see #setSeed
* @since Android 1.0
*/
public Random() {
setSeed(System.currentTimeMillis());
}
/**
* Construct a random generator with the given {@code seed} as the
* initial state.
*
* @param seed
* the seed that will determine the initial state of this random
* number generator.
* @see #setSeed
* @since Android 1.0
*/
public Random(long seed) {
setSeed(seed);
}
/**
* Returns a pseudo-random uniformly distributed {@code int} value of
* the number of bits specified by the argument {@code bits} as
* described by Donald E. Knuth in <i>The Art of Computer Programming,
* Volume 2: Seminumerical Algorithms</i>, section 3.2.1.
*
* @param bits
* number of bits of the returned value.
* @return a pseudo-random generated int number.
* @since Android 1.0
* @see #nextBytes
* @see #nextDouble
* @see #nextFloat
* @see #nextInt()
* @see #nextInt(int)
* @see #nextGaussian
* @see #nextLong
* @since Android 1.0
*/
protected synchronized int next(int bits) {
seed = (seed * multiplier + 0xbL) & ((1L << 48) - 1);
return (int) (seed >>> (48 - bits));
}
/**
* Returns the next pseudo-random, uniformly distributed {@code boolean} value
* generated by this generator.
*
* @return a pseudo-random, uniformly distributed boolean value.
* @since Android 1.0
*/
public boolean nextBoolean() {
return next(1) != 0;
}
/**
* Modifies the {@code byte} array by a random sequence of {@code byte}s generated by this
* random number generator.
*
* @param buf
* non-null array to contain the new random {@code byte}s.
* @see #next
* @since Android 1.0
*/
public void nextBytes(byte[] buf) {
int rand = 0, count = 0, loop = 0;
while (count < buf.length) {
if (loop == 0) {
rand = nextInt();
loop = 3;
} else {
loop--;
}
buf[count++] = (byte) rand;
rand >>= 8;
}
}
/**
* Generates a normally distributed random {@code double} number between 0.0
* inclusively and 1.0 exclusively.
*
* @return a random {@code double} in the range [0.0 - 1.0)
* @see #nextFloat
* @since Android 1.0
*/
public double nextDouble() {
return ((((long) next(26) << 27) + next(27)) / (double) (1L << 53));
}
/**
* Generates a normally distributed random {@code float} number between 0.0
* inclusively and 1.0 exclusively.
*
* @return float a random {@code float} number between [0.0 and 1.0)
* @see #nextDouble
* @since Android 1.0
*/
public float nextFloat() {
return (next(24) / 16777216f);
}
/**
* Pseudo-randomly generates (approximately) a normally distributed
* {@code double} value with mean 0.0 and a standard deviation value
* of {@code 1.0} using the <i>polar method<i> of G. E. P. Box, M.
* E. Muller, and G. Marsaglia, as described by Donald E. Knuth in <i>The
* Art of Computer Programming, Volume 2: Seminumerical Algorithms</i>,
* section 3.4.1, subsection C, algorithm P.
*
* @return a random {@code double}
* @see #nextDouble
* @since Android 1.0
*/
public synchronized double nextGaussian() {
if (haveNextNextGaussian) { // if X1 has been returned, return the
// second Gaussian
haveNextNextGaussian = false;
return nextNextGaussian;
}
double v1, v2, s;
do {
v1 = 2 * nextDouble() - 1; // Generates two independent random
// variables U1, U2
v2 = 2 * nextDouble() - 1;
s = v1 * v1 + v2 * v2;
} while (s >= 1);
double norm = Math.sqrt(-2 * Math.log(s) / s);
nextNextGaussian = v2 * norm; // should that not be norm instead
// of multiplier ?
haveNextNextGaussian = true;
return v1 * norm; // should that not be norm instead of multiplier
// ?
}
/**
* Generates a uniformly distributed 32-bit {@code int} value from
* the random number sequence.
*
* @return a uniformly distributed {@code int} value.
* @see java.lang.Integer#MAX_VALUE
* @see java.lang.Integer#MIN_VALUE
* @see #next
* @see #nextLong
* @since Android 1.0
*/
public int nextInt() {
return next(32);
}
/**
* Returns a new pseudo-random {@code int} value which is uniformly distributed
* between 0 (inclusively) and the value of {@code n} (exclusively).
*
* @param n
* the exclusive upper border of the range [0 - n).
* @return a random {@code int}.
* @since Android 1.0
*/
public int nextInt(int n) {
if (n > 0) {
if ((n & -n) == n) {
return (int) ((n * (long) next(31)) >> 31);
}
int bits, val;
do {
bits = next(31);
val = bits % n;
} while (bits - val + (n - 1) < 0);
return val;
}
throw new IllegalArgumentException();
}
/**
* Generates a uniformly distributed 64-bit integer value from
* the random number sequence.
*
* @return 64-bit random integer.
* @see java.lang.Integer#MAX_VALUE
* @see java.lang.Integer#MIN_VALUE
* @see #next
* @see #nextInt()
* @see #nextInt(int)
* @since Android 1.0
*/
public long nextLong() {
return ((long) next(32) << 32) + next(32);
}
/**
* Modifies the seed a using linear congruential formula presented in <i>The
* Art of Computer Programming, Volume 2</i>, Section 3.2.1.
*
* @param seed
* the seed that alters the state of the random number generator.
* @see #next
* @see #Random()
* @see #Random(long)
* @since Android 1.0
*/
public synchronized void setSeed(long seed) {
this.seed = (seed ^ multiplier) & ((1L << 48) - 1);
haveNextNextGaussian = false;
}
}
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