Fix cassandra-stress startup failure

patch by Jay Zhuang; reviewed by Blake Eggleston for CASSANDRA-14106

CHANGES.txt

@@ -1,4 +1,5 @@
 4.0
+ * Fix cassandra-stress startup failure (CASSANDRA-14106)
  * Remove initialDirectories from CFS (CASSANDRA-13928)
  * Fix trivial log format error (CASSANDRA-14015)
  * Allow sstabledump to do a json object per partition (CASSANDRA-13848)

tools/stress/src/org/apache/cassandra/stress/generate/Distribution.java

@@ -45,8 +45,8 @@ public abstract class Distribution implements Serializable
     public long average()
     {
         double sum = 0;
-        double d = 0d;
-        for (int count = 0; count < 50 ; count++)
+        float d = 0;
+        for (int count = 0; count < 51 ; count++)
         {
             sum += inverseCumProb(d);
             d += 0.02d;

tools/stress/test/unit/org/apache/cassandra/stress/generate/DistributionGaussianTest.java

@@ -0,0 +1,77 @@
+/*
+ * 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.cassandra.stress.generate;
+
+import org.junit.Test;
+
+import org.apache.cassandra.stress.settings.OptionDistribution;
+
+import static java.lang.Math.toIntExact;
+import static org.junit.Assert.*;
+
+public class DistributionGaussianTest
+{
+    @Test
+    public void simpleGaussian()
+    {
+        Distribution dist = OptionDistribution.get("gaussian(1..10)").get();
+        assertTrue(dist instanceof DistributionBoundApache);
+
+        assertEquals(1, dist.minValue());
+        assertEquals(10, dist.maxValue());
+        assertEquals(5, dist.average());
+
+        assertEquals(1, dist.inverseCumProb(0d));
+        assertEquals(10, dist.inverseCumProb(1d));
+
+        int testCount = 100000;
+        int[] results = new int[11];
+        for (int i = 0; i < testCount; i++)
+        {
+            int val = toIntExact(dist.next());
+            results[val]++;
+        }
+
+        // Increasing for the first half
+        for (int i = toIntExact(dist.minValue()); i < dist.average(); i++)
+        {
+            assertTrue(results[i] < results[i + 1]);
+        }
+
+        // Decreasing for the second half
+        for (int i = toIntExact(dist.average()) + 1; i < dist.maxValue(); i++)
+        {
+            assertTrue(results[i] > results[i + 1]);
+        }
+    }
+
+    @Test
+    public void negValueGaussian()
+    {
+        Distribution dist = OptionDistribution.get("gaussian(-1000..-10)").get();
+        assertTrue(dist instanceof DistributionBoundApache);
+
+        assertEquals(-1000, dist.minValue());
+        assertEquals( -10, dist.maxValue());
+        assertEquals(-504, dist.average());
+
+        assertEquals(-1000, dist.inverseCumProb(0d));
+        assertEquals(-10, dist.inverseCumProb(1d));
+    }
+}