Github user mateiz commented on a diff in the pull request:
https://github.com/apache/spark/pull/1520#discussion_r15215522
--- Diff:
mllib/src/main/scala/org/apache/spark/mllib/random/DistributionGenerator.scala
---
@@ -0,0 +1,105 @@
+/*
+ * 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.spark.mllib.random
+
+import cern.jet.random.Poisson
+import cern.jet.random.engine.DRand
+
+import org.apache.spark.util.random.{XORShiftRandom, Pseudorandom}
+
+/**
+ * Trait for random number generators that generate i.i.d values from a
distribution.
+ */
+trait DistributionGenerator extends Pseudorandom with Serializable {
+
+ /**
+ * @return An i.i.d sample as a Double from an underlying distribution.
+ */
+ def nextValue(): Double
+
+ /**
+ * @return A copy of the DistributionGenerator with a new instance of
the rng object used in the
+ * class when applicable. Each partition has a unique seed and
therefore requires its
+ * own instance of the DistributionGenerator.
+ */
+ def newInstance(): DistributionGenerator
+}
+
+/**
+ * Generates i.i.d. samples from U[0.0, 1.0]
+ */
+class UniformGenerator() extends DistributionGenerator {
+
+ // XORShiftRandom for better performance. Thread safety isn't necessary
here.
+ private val random = new XORShiftRandom()
+
+ /**
+ * @return An i.i.d sample as a Double from U[0.0, 1.0].
+ */
+ override def nextValue(): Double = {
+ random.nextDouble()
+ }
+
+ /** Set random seed. */
+ override def setSeed(seed: Long) = random.setSeed(seed)
+
+ override def newInstance(): UniformGenerator = new UniformGenerator()
+}
+
+/**
+ * Generates i.i.d. samples from the Standard Normal Distribution.
+ */
+class StandardNormalGenerator() extends DistributionGenerator {
+
+ // XORShiftRandom for better performance. Thread safety isn't necessary
here.
+ private val random = new XORShiftRandom()
--- End diff --
Is it allowed to use a DistributionGenerator before calling setSeed? It
would seem simpler to disallow that, but it seems to be something it got from
trait Pseudorandom.
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