[SPARK-13806] [SQL] fix rounding mode of negative float/double

## What changes were proposed in this pull request?

Round() in database usually round the number up (away from zero), it's different than Math.round() in Java.

For example:
```
scala> java.lang.Math.round(-3.5)
res3: Long = -3
```
In Database, we should return -4.0 in this cases.

This PR remove the buggy special case for scale=0.

## How was this patch tested?

Add tests for negative values with tie.

Author: Davies Liu <davies@databricks.com>

Closes #11894 from davies/fix_round.

2 files changed, 19 insertions, 33 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala
index 12fcc40376..e3d1bc127d 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala
@@ -748,7 +748,7 @@ case class Round(child: Expression, scale: Expression)
         if (f.isNaN || f.isInfinite) {
           f
         } else {
-          BigDecimal(f).setScale(_scale, HALF_UP).toFloat
+          BigDecimal(f.toDouble).setScale(_scale, HALF_UP).toFloat
         }
       case DoubleType =>
         val d = input1.asInstanceOf[Double]
@@ -804,39 +804,21 @@ case class Round(child: Expression, scale: Expression)
           s"${ev.value} = ${ce.value};"
         }
       case FloatType => // if child eval to NaN or Infinity, just return it.
-        if (_scale == 0) {
-          s"""
-            if (Float.isNaN(${ce.value}) || Float.isInfinite(${ce.value})) {
-              ${ev.value} = ${ce.value};
-            } else {
-              ${ev.value} = Math.round(${ce.value});
-            }"""
-        } else {
-          s"""
-            if (Float.isNaN(${ce.value}) || Float.isInfinite(${ce.value})) {
-              ${ev.value} = ${ce.value};
-            } else {
-              ${ev.value} = java.math.BigDecimal.valueOf(${ce.value}).
-                setScale(${_scale}, java.math.BigDecimal.ROUND_HALF_UP).floatValue();
-            }"""
-        }
+        s"""
+          if (Float.isNaN(${ce.value}) || Float.isInfinite(${ce.value})) {
+            ${ev.value} = ${ce.value};
+          } else {
+            ${ev.value} = java.math.BigDecimal.valueOf(${ce.value}).
+              setScale(${_scale}, java.math.BigDecimal.ROUND_HALF_UP).floatValue();
+          }"""
       case DoubleType => // if child eval to NaN or Infinity, just return it.
-        if (_scale == 0) {
-          s"""
-            if (Double.isNaN(${ce.value}) || Double.isInfinite(${ce.value})) {
-              ${ev.value} = ${ce.value};
-            } else {
-              ${ev.value} = Math.round(${ce.value});
-            }"""
-        } else {
-          s"""
-            if (Double.isNaN(${ce.value}) || Double.isInfinite(${ce.value})) {
-              ${ev.value} = ${ce.value};
-            } else {
-              ${ev.value} = java.math.BigDecimal.valueOf(${ce.value}).
-                setScale(${_scale}, java.math.BigDecimal.ROUND_HALF_UP).doubleValue();
-            }"""
-        }
+        s"""
+          if (Double.isNaN(${ce.value}) || Double.isInfinite(${ce.value})) {
+            ${ev.value} = ${ce.value};
+          } else {
+            ${ev.value} = java.math.BigDecimal.valueOf(${ce.value}).
+              setScale(${_scale}, java.math.BigDecimal.ROUND_HALF_UP).doubleValue();
+          }"""
     }
 
     if (scaleV == null) { // if scale is null, no need to eval its child at all
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 bd674dadd0..27195d3458 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
@@ -553,5 +553,9 @@ class MathFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper {
       checkEvaluation(Round(Literal.create(null, dataType),
         Literal.create(null, IntegerType)), null)
     }
+
+    checkEvaluation(Round(-3.5, 0), -4.0)
+    checkEvaluation(Round(-0.35, 1), -0.4)
+    checkEvaluation(Round(-35, -1), -40)
   }
 }