1 files changed, 76 insertions, 0 deletions
diff --git a/src/test/java/com/jsyn/util/TestPseudoRandom.java b/src/test/java/com/jsyn/util/TestPseudoRandom.java
new file mode 100644
index 0000000..b37475f
--- /dev/null
+++ b/src/test/java/com/jsyn/util/TestPseudoRandom.java
@@ -0,0 +1,76 @@
+/*
+ * Copyright 2009 Phil Burk, Mobileer Inc
+ *
+ * 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 com.jsyn.util;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class TestPseudoRandom {
+    PseudoRandom pseudoRandom;
+    private int[] bins;
+    private final static int BIN_SHIFTER = 8;
+    private final static int BIN_COUNT = 1 << BIN_SHIFTER;
+    private final static int BIN_MASK = BIN_COUNT - 1;
+
+    @Test
+    public void testMath() {
+        long seed = 3964771111L;
+        int positiveInt = (int) (seed & 0x7FFFFFFF);
+        assertTrue((positiveInt >= 0), "masked random positive, " + positiveInt);
+        double rand = positiveInt * (1.0 / (1L << 31));
+        assertTrue((rand >= 0.0), "not too low, " + rand);
+        assertTrue((rand < 1.0), "not too high, " + rand);
+    }
+
+    @Test
+    public void testIntegerDistribution() {
+        int scaler = 100;
+        for (int i = 0; i < (bins.length * scaler); i++) {
+            int rand = pseudoRandom.nextRandomInteger();
+            int positiveInt = rand & 0x7FFFFFFF;
+            assertTrue((positiveInt >= 0), "masked random " + positiveInt);
+            int index = (rand >> (32 - BIN_SHIFTER)) & BIN_MASK;
+            bins[index] += 1;
+        }
+        checkDistribution(scaler);
+    }
+
+    @Test
+    public void test01Distribution() {
+        int scaler = 100;
+        for (int i = 0; i < (bins.length * scaler); i++) {
+            double rand = pseudoRandom.random();
+            assertTrue((rand >= 0.0), "not too low, #" + i + " = " + rand);
+            assertTrue((rand < 1.0), "not too high, #" + i + " = " + rand);
+            int index = (int) (rand * BIN_COUNT);
+            bins[index] += 1;
+        }
+        checkDistribution(scaler);
+    }
+
+    private void checkDistribution(int scaler) {
+        // Generate running average that should stay near scaler
+        double average = scaler;
+        double coefficient = 0.9;
+        for (int i = 0; i < (bins.length); i++) {
+            average = (average * coefficient) + (bins[i] * (1.0 - coefficient));
+            assertEquals(scaler, average, 0.2 * scaler, "average at " + i);
+        }
+    }
+}