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-rw-r--r--src/main/java/org/rschwietzke/FastRandom.java76
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diff --git a/src/main/java/org/rschwietzke/FastRandom.java b/src/main/java/org/rschwietzke/FastRandom.java
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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);
+ }
+}