/**
* <h3>MersenneTwister and MersenneTwisterFast</h3>
* <p><b>Version 13</b>, based on version MT199937(99/10/29)
* of the Mersenne Twister algorithm found at
* <a href="http://www.math.keio.ac.jp/matumoto/emt.html">
* The Mersenne Twister Home Page</a>, with the initialization
* improved using the new 2002/1/26 initialization algorithm
* By Sean Luke, October 2004.
*
* <p><b>MersenneTwister</b> is a drop-in subclass replacement
* for java.util.Random. It is properly synchronized and
* can be used in a multithreaded environment. On modern VMs such
* as HotSpot, it is approximately 1/3 slower than java.util.Random.
*
* <p><b>MersenneTwisterFast</b> is not a subclass of java.util.Random. It has
* the same public methods as Random does, however, and it is
* algorithmically identical to MersenneTwister. MersenneTwisterFast
* has hard-code inlined all of its methods directly, and made all of them
* final (well, the ones of consequence anyway). Further, these
* methods are <i>not</i> synchronized, so the same MersenneTwisterFast
* instance cannot be shared by multiple threads. But all this helps
* MersenneTwisterFast achieve well over twice the speed of MersenneTwister.
* java.util.Random is about 1/3 slower than MersenneTwisterFast.
*
* <h3>About the Mersenne Twister</h3>
* <p>This is a Java version of the C-program for MT19937: Integer version.
* The MT19937 algorithm was created by Makoto Matsumoto and Takuji Nishimura,
* who ask: "When you use this, send an email to: matumoto@math.keio.ac.jp
* with an appropriate reference to your work". Indicate that this
* is a translation of their algorithm into Java.
*
* <p><b>Reference. </b>
* Makato Matsumoto and Takuji Nishimura,
* "Mersenne Twister: A 623-Dimensionally Equidistributed Uniform
* Pseudo-Random Number Generator",
* <i>ACM Transactions on Modeling and. Computer Simulation,</i>
* Vol. 8, No. 1, January 1998, pp 3--30.
*
* <h3>About this Version</h3>
*
* <p><b>Changes Since V12:</b> clone() method added.
*
* <p><b>Changes Since V11:</b> stateEquals(...) method added. MersenneTwisterFast
* is equal to other MersenneTwisterFasts with identical state; likewise
* MersenneTwister is equal to other MersenneTwister with identical state.
* This isn't equals(...) because that requires a contract of immutability
* to compare by value.
*
* <p><b>Changes Since V10:</b> A documentation error suggested that
* setSeed(int[]) required an int[] array 624 long. In fact, the array
* can be any non-zero length. The new version also checks for this fact.
*
* <p><b>Changes Since V9:</b> readState(stream) and writeState(stream)
* provided.
*
* <p><b>Changes Since V8:</b> setSeed(int) was only using the first 28 bits
* of the seed; it should have been 32 bits. For small-number seeds the
* behavior is identical.
*
* <p><b>Changes Since V7:</b> A documentation error in MersenneTwisterFast
* (but not MersenneTwister) stated that nextDouble selects uniformly from
* the full-open interval [0,1]. It does not. nextDouble's contract is
* identical across MersenneTwisterFast, MersenneTwister, and java.util.Random,
* namely, selection in the half-open interval [0,1). That is, 1.0 should
* not be returned. A similar contract exists in nextFloat.
*
* <p><b>Changes Since V6:</b> License has changed from LGPL to BSD.
* New timing information to compare against
* java.util.Random. Recent versions of HotSpot have helped Random increase
* in speed to the point where it is faster than MersenneTwister but slower
* than MersenneTwisterFast (which should be the case, as it's a less complex
* algorithm but is synchronized).
*
* <p><b>Changes Since V5:</b> New empty constructor made to work the same
* as java.util.Random -- namely, it seeds based on the current time in
* milliseconds.
*
* <p><b>Changes Since V4:</b> New initialization algorithms. See
* (see <a href="http://www.math.keio.ac.jp/matumoto/MT2002/emt19937ar.html"</a>
* http://www.math.keio.ac.jp/matumoto/MT2002/emt19937ar.html</a>)
*
* <p>The MersenneTwister code is based on standard MT19937 C/C++
* code by Takuji Nishimura,
* with suggestions from Topher Cooper and Marc Rieffel, July 1997.
* The code was originally translated into Java by Michael Lecuyer,
* January 1999, and the original code is Copyright (c) 1999 by Michael Lecuyer.
*
* <h3>Java notes</h3>
*
* <p>This implementation implements the bug fixes made
* in Java 1.2's version of Random, which means it can be used with
* earlier versions of Java. See
* <a href="http://www.javasoft.com/products/jdk/1.2/docs/api/java/util/Random.html">
* the JDK 1.2 java.util.Random documentation</a> for further documentation
* on the random-number generation contracts made. Additionally, there's
* an undocumented bug in the JDK java.util.Random.nextBytes() method,
* which this code fixes.
*
* <p> Just like java.util.Random, this
* generator accepts a long seed but doesn't use all of it. java.util.Random
* uses 48 bits. The Mersenne Twister instead uses 32 bits (int size).
* So it's best if your seed does not exceed the int range.
*
* <p>MersenneTwister can be used reliably
* on JDK version 1.1.5 or above. Earlier Java versions have serious bugs in
* java.util.Random; only MersenneTwisterFast (and not MersenneTwister nor
* java.util.Random) should be used with them.
*
* <h3>License</h3>
*
* Copyright (c) 2003 by Sean Luke. <br>
* Portions copyright (c) 1993 by Michael Lecuyer. <br>
* All rights reserved. <br>
*
* <p>Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* <ul>
* <li> Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* <li> Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* <li> Neither the name of the copyright owners, their employers, nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
* </ul>
* <p>THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNERS OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
@version 13
*/
package org.cojen.dirmi.util;
import java.security.SecureRandom;
// Note: this class is hard-inlined in all of its methods. This makes some of
// the methods well-nigh unreadable in their complexity. In fact, the Mersenne
// Twister is fairly easy code to understand: if you're trying to get a handle
// on the code, I strongly suggest looking at MersenneTwister.java first.
// -- Sean
// Changes made:
// - reformatted the code a bit
// - removed some methods
// - less inlining
// - added static utilities
//
// -- Brian S O'Neill
class MersenneTwisterFast {
private static final SecureRandom cSecureRandom = new SecureRandom();
private static final ThreadLocal<MersenneTwisterFast> cLocalInstance =
new ThreadLocal<MersenneTwisterFast>() {
@Override
public MersenneTwisterFast initialValue() {
return newInstance();
}
};
/**
* Returns a new non-thread safe instance.
*/
static MersenneTwisterFast newInstance() {
SecureRandom secure = cSecureRandom;
int[] seed = new int[N];
for (int i=0; i<seed.length; i++) {
seed[i] = secure.nextInt();
}
return new MersenneTwisterFast(seed);
}
/**
* Returns a non-sharable instance for this thread.
*/
static MersenneTwisterFast localInstance() {
return cLocalInstance.get();
}
// Period parameters
private static final int N = 624;
private static final int M = 397;
private static final int MATRIX_A = 0x9908b0df; // private static final * constant vector a
private static final int UPPER_MASK = 0x80000000; // most significant w-r bits
private static final int LOWER_MASK = 0x7fffffff; // least significant r bits
// Tempering parameters
private static final int TEMPERING_MASK_B = 0x9d2c5680;
private static final int TEMPERING_MASK_C = 0xefc60000;
private int mt[]; // the array for the state vector
private int mti; // mti==N+1 means mt[N] is not initialized
private int mag01[];
/**
* Constructor using a given seed. Though you pass this seed in
* as a long, it's best to make sure it's actually an integer.
*/
public MersenneTwisterFast(final long seed) {
setSeed(seed);
}
/**
* Constructor using an array of integers as seed.
* Your array must have a non-zero length. Only the first 624 integers
* in the array are used; if the array is shorter than this then
* integers are repeatedly used in a wrap-around fashion.
*/
public MersenneTwisterFast(final int[] array) {
setSeed(array);
}
/**
* Initalize the pseudo random number generator. Don't
* pass in a long that's bigger than an int (Mersenne Twister
* only uses the first 32 bits for its seed).
*/
public void setSeed(final long seed) {
mt = new int[N];
mag01 = new int[2];
mag01[0] = 0x0;
mag01[1] = MATRIX_A;
mt[0]= (int)(seed & 0xffffffff);
for (mti=1; mti<N; mti++) {
mt[mti] = (1812433253 * (mt[mti-1] ^ (mt[mti-1] >>> 30)) + mti);
/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
/* In the previous versions, MSBs of the seed affect */
/* only MSBs of the array mt[]. */
/* 2002/01/09 modified by Makoto Matsumoto */
}
}
/**
* Sets the seed of the MersenneTwister using an array of integers.
* Your array must have a non-zero length. Only the first 624 integers
* in the array are used; if the array is shorter than this then
* integers are repeatedly used in a wrap-around fashion.
*/
public void setSeed(final int[] array) {
if (array.length == 0) {
throw new IllegalArgumentException("Array length must be greater than zero");
}
int i, j, k;
setSeed(19650218);
i=1; j=0;
k = (N>array.length ? N : array.length);
for (; k!=0; k--) {
mt[i] = (mt[i] ^ ((mt[i-1] ^ (mt[i-1] >>> 30)) * 1664525)) + array[j] + j; /* non linear */
i++;
j++;
if (i>=N) { mt[0] = mt[N-1]; i=1; }
if (j>=array.length) j=0;
}
for (k=N-1; k!=0; k--) {
mt[i] = (mt[i] ^ ((mt[i-1] ^ (mt[i-1] >>> 30)) * 1566083941)) - i; /* non linear */
i++;
if (i>=N) {
mt[0] = mt[N-1]; i=1;
}
}
mt[0] = 0x80000000; /* MSB is 1; assuring non-zero initial array */
}
public final int nextInt() {
int y;
if (mti >= N) { // generate N words at one time
int kk;
final int[] mt = this.mt; // locals are slightly faster
final int[] mag01 = this.mag01; // locals are slightly faster
for (kk = 0; kk < N - M; kk++) {
y = (mt[kk] & UPPER_MASK) | (mt[kk+1] & LOWER_MASK);
mt[kk] = mt[kk+M] ^ (y >>> 1) ^ mag01[y & 0x1];
}
for (; kk < N-1; kk++) {
y = (mt[kk] & UPPER_MASK) | (mt[kk+1] & LOWER_MASK);
mt[kk] = mt[kk+(M-N)] ^ (y >>> 1) ^ mag01[y & 0x1];
}
y = (mt[N-1] & UPPER_MASK) | (mt[0] & LOWER_MASK);
mt[N-1] = mt[M-1] ^ (y >>> 1) ^ mag01[y & 0x1];
mti = 0;
}
y = mt[mti++];
y ^= y >>> 11; // TEMPERING_SHIFT_U(y)
y ^= (y << 7) & TEMPERING_MASK_B; // TEMPERING_SHIFT_S(y)
y ^= (y << 15) & TEMPERING_MASK_C; // TEMPERING_SHIFT_T(y)
y ^= (y >>> 18); // TEMPERING_SHIFT_L(y)
return y;
}
/** Returns an integer drawn uniformly from 0 to n-1. Suffice it to say,
n must be > 0, or an IllegalArgumentException is raised. */
public final int nextInt(final int n) {
if (n <= 0) {
throw new IllegalArgumentException("n must be > 0");
}
if ((n & -n) == n) { // i.e., n is a power of 2
return (int)((n * (long) (nextInt() >>> 1) ) >> 31);
}
int bits, val;
do {
bits = (nextInt() >>> 1);
val = bits % n;
} while (bits - val + n - 1 < 0);
return val;
}
public final void nextBytes(byte[] bytes) {
for (int i = 0; i < bytes.length; ) {
for (int rnd = nextInt(), n = Math.min(bytes.length - i, 4); n-- > 0; rnd >>= 8) {
bytes[i++] = (byte) rnd;
}
}
}
public final long nextLong() {
return (((long) nextInt()) << 32) + (long) nextInt();
}
/** Returns a long drawn uniformly from 0 to n-1. Suffice it to say,
n must be > 0, or an IllegalArgumentException is raised. */
public final long nextLong(final long n) {
if (n <= 0) {
throw new IllegalArgumentException("n must be > 0");
}
long bits, val;
do {
bits = (((((long) nextInt()) << 32) + (long) nextInt()) >>> 1);
val = bits % n;
} while (bits - val + n - 1 < 0);
return val;
}
/** Returns a random double in the half-open range from [0.0,1.0). Thus 0.0 is a valid
result but 1.0 is not. */
public final double nextDouble() {
/* derived from nextDouble documentation in jdk 1.2 docs, see top */
return ((((long) (nextInt() >>> 6)) << 27) + (nextInt() >>> 5)) / (double) (1L << 53);
}
/** Returns a random float in the half-open range from [0.0f,1.0f). Thus 0.0f is a valid
result but 1.0f is not. */
public final float nextFloat() {
return (nextInt() >>> 8) / ((float) (1 << 24));
}
public final boolean nextBoolean() {
return (nextInt() >>> 31) != 0;
}
}