1 files changed, 108 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math/random/Well19937a.java b/src/main/java/org/apache/commons/math/random/Well19937a.java
new file mode 100644
index 0000000..97f9bfd
--- /dev/null
+++ b/src/main/java/org/apache/commons/math/random/Well19937a.java
@@ -0,0 +1,108 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.commons.math.random;
+
+
+/** This class implements the WELL19937a pseudo-random number generator
+ * from Fran&ccedil;ois Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
+
+ * <p>This generator is described in a paper by Fran&ccedil;ois Panneton,
+ * Pierre L'Ecuyer and Makoto Matsumoto <a
+ * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
+ * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
+ * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
+ * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p>
+
+ * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
+ * @version $Revision: 1003892 $ $Date: 2010-10-02 23:28:56 +0200 (sam. 02 oct. 2010) $
+ * @since 2.2
+
+ */
+public class Well19937a extends AbstractWell {
+
+    /** Serializable version identifier. */
+    private static final long serialVersionUID = -7462102162223815419L;
+
+    /** Number of bits in the pool. */
+    private static final int K = 19937;
+
+    /** First parameter of the algorithm. */
+    private static final int M1 = 70;
+
+    /** Second parameter of the algorithm. */
+    private static final int M2 = 179;
+
+    /** Third parameter of the algorithm. */
+    private static final int M3 = 449;
+
+    /** Creates a new random number generator.
+     * <p>The instance is initialized using the current time as the
+     * seed.</p>
+     */
+    public Well19937a() {
+        super(K, M1, M2, M3);
+    }
+
+    /** Creates a new random number generator using a single int seed.
+     * @param seed the initial seed (32 bits integer)
+     */
+    public Well19937a(int seed) {
+        super(K, M1, M2, M3, seed);
+    }
+
+    /** Creates a new random number generator using an int array seed.
+     * @param seed the initial seed (32 bits integers array), if null
+     * the seed of the generator will be related to the current time
+     */
+    public Well19937a(int[] seed) {
+        super(K, M1, M2, M3, seed);
+    }
+
+    /** Creates a new random number generator using a single long seed.
+     * @param seed the initial seed (64 bits integer)
+     */
+    public Well19937a(long seed) {
+        super(K, M1, M2, M3, seed);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    protected int next(final int bits) {
+
+        final int indexRm1 = iRm1[index];
+        final int indexRm2 = iRm2[index];
+
+        final int v0       = v[index];
+        final int vM1      = v[i1[index]];
+        final int vM2      = v[i2[index]];
+        final int vM3      = v[i3[index]];
+
+        final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
+        final int z1 = (v0 ^ (v0 << 25))  ^ (vM1 ^ (vM1 >>> 27));
+        final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
+        final int z3 = z1      ^ z2;
+        final int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));
+
+        v[index]     = z3;
+        v[indexRm1]  = z4;
+        v[indexRm2] &= 0x80000000;
+        index        = indexRm1;
+
+        return z4 >>> (32 - bits);
+
+    }
+}