[commons-rng] branch master updated: Add edge case where the generator outputs all bits set.

[aherbert]

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aherbert pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-rng.git


The following commit(s) were added to refs/heads/master by this push:
     new c7779b1  Add edge case where the generator outputs all bits set.
c7779b1 is described below

commit c7779b1e32ce3533d2f9f440b46106bb1907be46
Author: aherbert <aherb...@apache.org>
AuthorDate: Fri Jun 11 13:05:02 2021 +0100

    Add edge case where the generator outputs all bits set.
---
 .../AhrensDieterExponentialSamplerTest.java        | 23 +++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git 
a/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/distribution/AhrensDieterExponentialSamplerTest.java
 
b/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/distribution/AhrensDieterExponentialSamplerTest.java
index d7b81a8..8ce972d 100644
--- 
a/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/distribution/AhrensDieterExponentialSamplerTest.java
+++ 
b/commons-rng-sampling/src/test/java/org/apache/commons/rng/sampling/distribution/AhrensDieterExponentialSamplerTest.java
@@ -22,6 +22,7 @@ import org.apache.commons.rng.UniformRandomProvider;
 import org.apache.commons.rng.core.source64.SplitMix64;
 import org.apache.commons.rng.sampling.RandomAssert;
 import org.apache.commons.rng.simple.RandomSource;
+import org.junit.Assert;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.Timeout;
@@ -75,6 +76,26 @@ public class AhrensDieterExponentialSamplerTest {
         };
         final SharedStateContinuousSampler sampler = 
AhrensDieterExponentialSampler.of(rng, 1);
         // This should not infinite loop
-        sampler.sample();
+        final double x = sampler.sample();
+        Assert.assertTrue(x >= 0);
+    }
+
+    /**
+     * Test the sampler is robust to a generator that outputs full bits. The 
uniform random
+     * double will be at the top of the range {@code [0, 1]}.
+     */
+    @Test
+    public void testSamplerWithOneFromRandomGenerator() {
+        // A broken generator that returns zero.
+        final UniformRandomProvider rng = new SplitMix64(0) {
+            @Override
+            public long nextLong() {
+                // All the bits set
+                return -1;
+            }
+        };
+        final SharedStateContinuousSampler sampler = 
AhrensDieterExponentialSampler.of(rng, 1);
+        final double x = sampler.sample();
+        Assert.assertTrue(x >= 0);
     }
 }