implement Java 17 j.u.r.RandomGenerator#nextExponential()

stefan-zobel · Sep 18, 2021 · a36de70 · a36de70
1 parent aa1d002
commit a36de70
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diff --git a/src/main/java/java8/util/SplittableRandom.java b/src/main/java/java8/util/SplittableRandom.java
@@ -845,6 +845,22 @@ public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound)
              false);
     }
 
+    /**
+     * Returns a nonnegative {@code double} value pseudorandomly chosen from
+     * an exponential distribution whose mean is 1.
+     *
+     * @return a nonnegative {@code double} value pseudorandomly chosen from an
+     *         exponential distribution
+     * @since 17
+     */
+    public double nextExponential() {
+        double u;
+        do {
+            u = nextDouble();
+        } while (u == 0.0 || u == 1.0);
+        return -Math.log(u);
+    }
+
     /**
      * Return true if the implementation of RandomGenerator (algorithm) has been
      * marked for deprecation.
@@ -858,7 +874,6 @@ public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound)
      *
      * @return true if the implementation of RandomGenerator (algorithm) has been
      *         marked for deprecation
-     *
      * @since 17
      */
     public boolean isDeprecated() {

diff --git a/src/main/java/java8/util/concurrent/ThreadLocalRandom.java b/src/main/java/java8/util/concurrent/ThreadLocalRandom.java
@@ -732,6 +732,22 @@ public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound)
              false);
     }
 
+    /**
+     * Returns a nonnegative {@code double} value pseudorandomly chosen from
+     * an exponential distribution whose mean is 1.
+     *
+     * @return a nonnegative {@code double} value pseudorandomly chosen from an
+     *         exponential distribution
+     * @since 17
+     */
+    public double nextExponential() {
+        double u;
+        do {
+            u = nextDouble();
+        } while (u == 0.0 || u == 1.0);
+        return -Math.log(u);
+    }
+
     /**
      * Return true if the implementation of RandomGenerator (algorithm) has been
      * marked for deprecation.
@@ -745,7 +761,6 @@ public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound)
      *
      * @return true if the implementation of RandomGenerator (algorithm) has been
      *         marked for deprecation
-     *
      * @since 17
      */
     public boolean isDeprecated() {