[SPARK-8218][SQL] Binary log math function update.

Some minor updates based on after merging #6725.

Author: Reynold Xin <rxin@databricks.com>

Closes #6871 from rxin/log and squashes the following commits:

ab51542 [Reynold Xin] Use JVM log
76fc8de [Reynold Xin] Fixed arg.
a7c1522 [Reynold Xin] [SPARK-8218][SQL] Binary log math function update.

1 files changed, 4 insertions, 0 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala
index 3b83c6da0e..f79bf4aee0 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala
@@ -260,6 +260,10 @@ case class Pow(left: Expression, right: Expression)
 
 case class Logarithm(left: Expression, right: Expression)
   extends BinaryMathExpression((c1, c2) => math.log(c2) / math.log(c1), "LOG") {
+
+  /**
+   * Natural log, i.e. using e as the base.
+   */
   def this(child: Expression) = {
     this(EulerNumber(), child)
   }