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/*
* Copyright 2023 The original authors
*
* Licensed 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.rschwietzke;
/**
* Ultra-fast pseudo random generator that is not synchronized!
* Don't use anything from Random by inheritance, this will inherit
* a volatile! Not my idea, copyied in parts some demo random
* generator lessons.
*
* @author rschwietzke
*
*/
public class FastRandom {
private long seed;
public FastRandom() {
this.seed = System.currentTimeMillis();
}
public FastRandom(long seed) {
this.seed = seed;
}
protected int next(int nbits) {
// N.B. Not thread-safe!
long x = this.seed;
x ^= (x << 21);
x ^= (x >>> 35);
x ^= (x << 4);
this.seed = x;
x &= ((1L << nbits) - 1);
return (int) x;
}
/**
* Borrowed from the JDK
*
* @param bound
* @return
*/
public int nextInt(int bound) {
int r = next(31);
int m = bound - 1;
if ((bound & m) == 0) // i.e., bound is a power of 2
r = (int) ((bound * (long) r) >> 31);
else {
for (int u = r; u - (r = u % bound) + m < 0; u = next(31))
;
}
return r;
}
/**
* Borrowed from the JDK
* @return
*/
public int nextInt() {
return next(32);
}
}
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