Reverting commit ffae3bdbb6 as per Gilles request.

The work on revamping the random packages is perfoemd in the random-ravamp branch.

src/main/java/org/apache/commons/math4/random/AbstractWell.java

@@ -34,12 +34,10 @@ import org.apache.commons.math4.util.FastMath;
  * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
  * @since 2.2
  */
-public abstract class AbstractWell
-    extends BaseRandomGenerator
-    implements Serializable {
+public abstract class AbstractWell extends BitsStreamGenerator implements Serializable {
 
     /** Serializable version identifier. */
-    private static final long serialVersionUID = 20150228L;
+    private static final long serialVersionUID = 20150223L;
 
     /** Current index in the bytes pool. */
     protected int index;
@@ -135,6 +133,10 @@ public abstract class AbstractWell
         setSeed(new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) });
     }
 
+    /** {@inheritDoc} */
+    @Override
+    protected abstract int next(final int bits);
+
     /** Calculate the number of 32-bits blocks.
      * @param k number of bits in the pool (not necessarily a multiple of 32)
      * @return the number of 32-bits blocks

src/main/java/org/apache/commons/math4/random/Well1024a.java

@@ -16,18 +16,15 @@
  */
 package org.apache.commons.math4.random;
 
-/**
- * This class implements the WELL1024a pseudo-random number generator
+/** This class implements the WELL1024a pseudo-random number generator
  * from François 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>
+ * 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>
  * @since 2.2
@@ -84,7 +81,8 @@ public class Well1024a extends AbstractWell {
 
     /** {@inheritDoc} */
     @Override
-    public int nextInt() {
+    protected int next(final int bits) {
+
         final int indexRm1 = TABLE.getIndexPred(index);
 
         final int v0       = v[index];
@@ -102,6 +100,8 @@ public class Well1024a extends AbstractWell {
         v[indexRm1]  = z4;
         index        = indexRm1;
 
-        return z4;
+        return z4 >>> (32 - bits);
+
     }
+
 }

src/main/java/org/apache/commons/math4/random/Well19937a.java

@@ -82,7 +82,7 @@ public class Well19937a extends AbstractWell {
 
     /** {@inheritDoc} */
     @Override
-    public int nextInt() {
+    protected int next(final int bits) {
 
         final int indexRm1 = TABLE.getIndexPred(index);
         final int indexRm2 = TABLE.getIndexPred2(index);
@@ -103,6 +103,8 @@ public class Well19937a extends AbstractWell {
         v[indexRm2] &= 0x80000000;
         index        = indexRm1;
 
-        return z4;
+        return z4 >>> (32 - bits);
+
     }
+
 }

src/main/java/org/apache/commons/math4/random/Well19937c.java

@@ -82,7 +82,7 @@ public class Well19937c extends AbstractWell {
 
     /** {@inheritDoc} */
     @Override
-    public int nextInt() {
+    protected int next(final int bits) {
 
         final int indexRm1 = TABLE.getIndexPred(index);
         final int indexRm2 = TABLE.getIndexPred2(index);
@@ -108,6 +108,8 @@ public class Well19937c extends AbstractWell {
         z4 ^= (z4 <<  7) & 0xe46e1700;
         z4 ^= (z4 << 15) & 0x9b868000;
 
-        return z4;
+        return z4 >>> (32 - bits);
+
     }
+
 }

src/main/java/org/apache/commons/math4/random/Well44497a.java

@@ -81,7 +81,7 @@ public class Well44497a extends AbstractWell {
 
     /** {@inheritDoc} */
     @Override
-    public int nextInt() {
+    protected int next(final int bits) {
 
         final int indexRm1 = TABLE.getIndexPred(index);
         final int indexRm2 = TABLE.getIndexPred2(index);
@@ -105,6 +105,8 @@ public class Well44497a extends AbstractWell {
         v[indexRm2] &= 0xFFFF8000;
         index        = indexRm1;
 
-        return z4;
+        return z4 >>> (32 - bits);
+
     }
+
 }

src/main/java/org/apache/commons/math4/random/Well44497b.java

@@ -81,7 +81,7 @@ public class Well44497b extends AbstractWell {
 
     /** {@inheritDoc} */
     @Override
-    public int nextInt() {
+    protected int next(final int bits) {
 
         // compute raw value given by WELL44497a generator
         // which is NOT maximally-equidistributed
@@ -112,6 +112,8 @@ public class Well44497b extends AbstractWell {
         z4 ^= (z4 <<  7) & 0x93dd1400;
         z4 ^= (z4 << 15) & 0xfa118000;
 
-        return z4;
+        return z4 >>> (32 - bits);
+
     }
+
 }

src/main/java/org/apache/commons/math4/random/Well512a.java

@@ -82,7 +82,7 @@ public class Well512a extends AbstractWell {
 
     /** {@inheritDoc} */
     @Override
-    public int nextInt() {
+    protected int next(final int bits) {
 
         final int indexRm1 = TABLE.getIndexPred(index);
 
@@ -101,6 +101,8 @@ public class Well512a extends AbstractWell {
         v[indexRm1]  = z4;
         index    = indexRm1;
 
-        return z4;
+        return z4 >>> (32 - bits);
+
     }
+
 }

src/test/java/org/apache/commons/math4/random/Well1024aTest.java

@@ -21,7 +21,7 @@ import org.apache.commons.math4.random.Well1024a;
 import org.junit.Assert;
 import org.junit.Test;
 
-public class Well1024aTest extends BaseRandomGeneratorTest {
+public class Well1024aTest extends RandomGeneratorAbstractTest {
 
     @Override
     protected RandomGenerator makeGenerator() {

src/test/java/org/apache/commons/math4/random/Well19937aTest.java

@@ -21,7 +21,7 @@ import org.apache.commons.math4.random.Well19937a;
 import org.junit.Assert;
 import org.junit.Test;
 
-public class Well19937aTest extends BaseRandomGeneratorTest {
+public class Well19937aTest extends RandomGeneratorAbstractTest {
 
     @Override
     public RandomGenerator makeGenerator() {

src/test/java/org/apache/commons/math4/random/Well19937cTest.java

@@ -21,7 +21,7 @@ import org.apache.commons.math4.random.Well19937c;
 import org.junit.Assert;
 import org.junit.Test;
 
-public class Well19937cTest extends BaseRandomGeneratorTest {
+public class Well19937cTest extends RandomGeneratorAbstractTest {
 
     @Override
     public RandomGenerator makeGenerator() {

src/test/java/org/apache/commons/math4/random/Well44497aTest.java

@@ -21,7 +21,7 @@ import org.apache.commons.math4.random.Well44497a;
 import org.junit.Assert;
 import org.junit.Test;
 
-public class Well44497aTest extends BaseRandomGeneratorTest {
+public class Well44497aTest extends RandomGeneratorAbstractTest {
 
     @Override
     public RandomGenerator makeGenerator() {

src/test/java/org/apache/commons/math4/random/Well44497bTest.java

@@ -21,7 +21,7 @@ import org.apache.commons.math4.random.Well44497b;
 import org.junit.Assert;
 import org.junit.Test;
 
-public class Well44497bTest extends BaseRandomGeneratorTest {
+public class Well44497bTest extends RandomGeneratorAbstractTest {
 
     @Override
     public RandomGenerator makeGenerator() {

src/test/java/org/apache/commons/math4/random/Well512aTest.java

@@ -21,7 +21,7 @@ import org.apache.commons.math4.random.Well512a;
 import org.junit.Assert;
 import org.junit.Test;
 
-public class Well512aTest extends BaseRandomGeneratorTest {
+public class Well512aTest extends RandomGeneratorAbstractTest {
 
     @Override
     public RandomGenerator makeGenerator() {