[SPARK-8217] [SQL] math function log2

Author: Daoyuan Wang <daoyuan.wang@intel.com>

This patch had conflicts when merged, resolved by
Committer: Reynold Xin <rxin@databricks.com>

Closes #6718 from adrian-wang/udflog2 and squashes the following commits:

3909f48 [Daoyuan Wang] math function: log2

3 files changed, 24 insertions, 0 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala
index 39875d7f21..a7816e3275 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala
@@ -111,6 +111,7 @@ object FunctionRegistry {
     expression[Log10]("log10"),
     expression[Log1p]("log1p"),
     expression[Pi]("pi"),
+    expression[Log2]("log2"),
     expression[Pow]("pow"),
     expression[Rint]("rint"),
     expression[Signum]("signum"),
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 e1d8c9a0cd..97e960b8d6 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
@@ -161,6 +161,23 @@ case class Floor(child: Expression) extends UnaryMathExpression(math.floor, "FLO
 
 case class Log(child: Expression) extends UnaryMathExpression(math.log, "LOG")
 
+case class Log2(child: Expression)
+  extends UnaryMathExpression((x: Double) => math.log(x) / math.log(2), "LOG2") {
+  override def genCode(ctx: CodeGenContext, ev: GeneratedExpressionCode): String = {
+    val eval = child.gen(ctx)
+    eval.code + s"""
+      boolean ${ev.isNull} = ${eval.isNull};
+      ${ctx.javaType(dataType)} ${ev.primitive} = ${ctx.defaultValue(dataType)};
+      if (!${ev.isNull}) {
+        ${ev.primitive} = java.lang.Math.log(${eval.primitive}) / java.lang.Math.log(2);
+        if (Double.valueOf(${ev.primitive}).isNaN()) {
+          ${ev.isNull} = true;
+        }
+      }
+    """
+  }
+}
+
 case class Log10(child: Expression) extends UnaryMathExpression(math.log10, "LOG10")
 
 case class Log1p(child: Expression) extends UnaryMathExpression(math.log1p, "LOG1P")
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathFunctionsSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathFunctionsSuite.scala
index 1fe69059d3..864c954ee8 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathFunctionsSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathFunctionsSuite.scala
@@ -185,6 +185,12 @@ class MathFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper {
     testUnary(Log1p, math.log1p, (-10 to -2).map(_ * 1.0), expectNull = true)
   }
 
+  test("log2") {
+    def f: (Double) => Double = (x: Double) => math.log(x) / math.log(2)
+    testUnary(Log2, f, (0 to 20).map(_ * 0.1))
+    testUnary(Log2, f, (-5 to -1).map(_ * 1.0), expectNull = true)
+  }
+
   test("pow") {
     testBinary(Pow, math.pow, (-5 to 5).map(v => (v * 1.0, v * 1.0)))
     testBinary(Pow, math.pow, Seq((-1.0, 0.9), (-2.2, 1.7), (-2.2, -1.7)), expectNull = true)