Faster version of the data generator

1 files changed, 76 insertions, 0 deletions

diff --git a/src/main/java/org/rschwietzke/FastRandom.java b/src/main/java/org/rschwietzke/FastRandom.java
new file mode 100644
index 0000000..2d25d35
--- /dev/null
+++ b/src/main/java/org/rschwietzke/FastRandom.java
@@ -0,0 +1,76 @@
+/*
+ *  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);
+    }
+}