[SPARK-8945][SQL] Add add and subtract expressions for IntervalType

JIRA: https://issues.apache.org/jira/browse/SPARK-8945

Add add and subtract expressions for IntervalType.

Author: Liang-Chi Hsieh <viirya@appier.com>

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

Closes #7398 from viirya/interval_add_subtract and squashes the following commits:

acd1f1e [Liang-Chi Hsieh] Merge remote-tracking branch 'upstream/master' into interval_add_subtract
5abae28 [Liang-Chi Hsieh] For comments.
6f5b72e [Liang-Chi Hsieh] Merge remote-tracking branch 'upstream/master' into interval_add_subtract
dbe3906 [Liang-Chi Hsieh] For comments.
13a2fc5 [Liang-Chi Hsieh] Merge remote-tracking branch 'upstream/master' into interval_add_subtract
83ec129 [Liang-Chi Hsieh] Remove intervalMethod.
acfe1ab [Liang-Chi Hsieh] Fix scala style.
d3e9d0e [Liang-Chi Hsieh] Add add and subtract expressions for IntervalType.

1 files changed, 16 insertions, 0 deletions

diff --git a/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java b/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java
index 905ea0b7b8..71b1a85a81 100644
--- a/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java
+++ b/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java
@@ -87,6 +87,22 @@ public final class Interval implements Serializable {
     this.microseconds = microseconds;
   }
 
+  public Interval add(Interval that) {
+    int months = this.months + that.months;
+    long microseconds = this.microseconds + that.microseconds;
+    return new Interval(months, microseconds);
+  }
+
+  public Interval subtract(Interval that) {
+    int months = this.months - that.months;
+    long microseconds = this.microseconds - that.microseconds;
+    return new Interval(months, microseconds);
+  }
+
+  public Interval negate() {
+    return new Interval(-this.months, -this.microseconds);
+  }
+
   @Override
   public boolean equals(Object other) {
     if (this == other) return true;