package org.jgap.util;
/**
Implementation of a <b>randomX</b>-compliant class using the
"Minimal Standard" multiplicative congruential generator of Park
and Miller. [Park, S.K. and K.W. Miller, <cite>Communications of
the ACM</cite> <b>31</b>, 1192-1201 (1988).]
<p>
The generation algorithm is:
<p>
<center>
<em>I<sub>j+1</sub></em> = (<em>I<sub>j</sub></em> 16807) & 0x7FFFFFFF
</center>
<p>
Note that the intermediate value of the multiplication by 16807
(7<sup>5</sup>) exceeds that representable in 32 bits; this has
deterred use of this generator in most portable languages.
Fortunately, Java's <tt>long</tt> type is guaranteed to be
64 bits, so a straightforward and portable implementation is
possible.
<p>
Designed and implemented in July 1996 by
<a href="http://www.fourmilab.ch/">John Walker</a>,
<a href="mailto:kelvin@fourmilab.ch">kelvin@fourmilab.ch</a>.
*/
public class randomMCG extends randomX {
long state;
// Constructors
/** Creates a new pseudorandom number generator, seeded from
the current time. */
public randomMCG() {
this.setSeed(System.currentTimeMillis());
}
/** Creates a new pseudorandom number generator with a
specified nonzero seed.
@param seed initial seed for the generator
*/
public randomMCG(long seed) throws IllegalArgumentException {
this.setSeed(seed);
}
// Seed access
/** Set seed for generator. Subsequent values will be based
on the given nonzero seed.
@param seed seed for the generator
*/
public void setSeed(long seed) throws IllegalArgumentException {
int i;
if (seed == 0) {
throw new IllegalArgumentException("seed must be nonzero");
}
super.setSeed(); // Notify parent seed has changed
state = seed & 0xFFFFFFFFL;
for (i = 0; i < 11; i++) {
nextByte();
}
}
/** Get next byte from generator.
@return the next byte from the generator.
*/
public byte nextByte() {
state = (state * 16807) & 0x7FFFFFFFL;
return (byte) ((state >> 11) & 0xFF);
}
};
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