1 files changed, 76 insertions, 0 deletions
diff --git a/src/de/lmu/ifi/dbs/elki/math/random/FastNonThreadsafeRandom.java b/src/de/lmu/ifi/dbs/elki/math/random/FastNonThreadsafeRandom.java
new file mode 100644
index 00000000..da1c01fa
--- /dev/null
+++ b/src/de/lmu/ifi/dbs/elki/math/random/FastNonThreadsafeRandom.java
@@ -0,0 +1,76 @@
+package de.lmu.ifi.dbs.elki.math.random;
+
+/*
+ This file is part of ELKI:
+ Environment for Developing KDD-Applications Supported by Index-Structures
+
+ Copyright (C) 2014
+ Ludwig-Maximilians-Universität München
+ Lehr- und Forschungseinheit für Datenbanksysteme
+ ELKI Development Team
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Affero General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU Affero General Public License for more details.
+
+ You should have received a copy of the GNU Affero General Public License
+ along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+import java.util.Random;
+
+/**
+ * Drop-in replacement for {@link java.util.Random}, but not using atomic long
+ * seeds. This implementation is <em>no longer thread-safe</em> (but faster)!
+ * 
+ * @author Erich Schubert
+ */
+public class FastNonThreadsafeRandom extends Random {
+  /**
+   * Serial version number.
+   */
+  private static final long serialVersionUID = 1L;
+
+  // These are the same constants as in {@link java.util.Random}
+  // since we want to leave the random sequence unchanged.
+  private static final long multiplier = 0x5DEECE66DL, addend = 0xBL,
+      mask = (1L << 48) - 1;
+
+  /**
+   * The random seed. We can't use super.seed.
+   */
+  private long seed;
+
+  /**
+   * Constructor called only by localRandom.initialValue.
+   */
+  public FastNonThreadsafeRandom() {
+    super();
+  }
+
+  /**
+   * Constructor.
+   * 
+   * @param seed Random generator seed.
+   */
+  public FastNonThreadsafeRandom(long seed) {
+    this.seed = (seed ^ multiplier) & mask;
+  }
+
+  @Override
+  public void setSeed(long seed) {
+    this.seed = (seed ^ multiplier) & mask;
+  }
+
+  @Override
+  protected int next(int bits) {
+    // Linear Congruential Generator:
+    seed = (seed * multiplier + addend) & mask;
+    return (int) (seed >>> (48 - bits));
+  }
+}