[SPARK-19180] [SQL] the offset of short should be 2 in OffHeapColumn

## What changes were proposed in this pull request?

the offset of short is 4 in OffHeapColumnVector's putShorts, but actually it should be 2.

## How was this patch tested?

unit test

Author: Yucai Yu <yucai.yu@intel.com>

Closes #16555 from yucai/offheap_short.

(cherry picked from commit ad0dadaa)
Signed-off-by: Davies Liu <davies.liu@gmail.com>

sql/core/src/main/java/org/apache/spark/sql/execution/vectorized/OffHeapColumnVector.java

@@ -177,7 +177,7 @@ public final class OffHeapColumnVector extends ColumnVector {
   @Override
   public void putShorts(int rowId, int count, short value) {
     long offset = data + 2 * rowId;
-    for (int i = 0; i < count; ++i, offset += 4) {
+    for (int i = 0; i < count; ++i, offset += 2) {
       Platform.putShort(null, offset, value);
     }
   }

sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala

@@ -119,6 +119,69 @@ class ColumnarBatchSuite extends SparkFunSuite {
     }}
   }
 
+  test("Short Apis") {
+    (MemoryMode.ON_HEAP :: MemoryMode.OFF_HEAP :: Nil).foreach { memMode => {
+      val seed = System.currentTimeMillis()
+      val random = new Random(seed)
+      val reference = mutable.ArrayBuffer.empty[Short]
+
+      val column = ColumnVector.allocate(1024, ShortType, memMode)
+      var idx = 0
+
+      val values = (1 :: 2 :: 3 :: 4 :: 5 :: Nil).map(_.toShort).toArray
+      column.putShorts(idx, 2, values, 0)
+      reference += 1
+      reference += 2
+      idx += 2
+
+      column.putShorts(idx, 3, values, 2)
+      reference += 3
+      reference += 4
+      reference += 5
+      idx += 3
+
+      column.putShort(idx, 9)
+      reference += 9
+      idx += 1
+
+      column.putShorts(idx, 3, 4)
+      reference += 4
+      reference += 4
+      reference += 4
+      idx += 3
+
+      while (idx < column.capacity) {
+        val single = random.nextBoolean()
+        if (single) {
+          val v = random.nextInt().toShort
+          column.putShort(idx, v)
+          reference += v
+          idx += 1
+        } else {
+          val n = math.min(random.nextInt(column.capacity / 20), column.capacity - idx)
+          val v = (n + 1).toShort
+          column.putShorts(idx, n, v)
+          var i = 0
+          while (i < n) {
+            reference += v
+            i += 1
+          }
+          idx += n
+        }
+      }
+
+      reference.zipWithIndex.foreach { v =>
+        assert(v._1 == column.getShort(v._2), "Seed = " + seed + " Mem Mode=" + memMode)
+        if (memMode == MemoryMode.OFF_HEAP) {
+          val addr = column.valuesNativeAddress()
+          assert(v._1 == Platform.getShort(null, addr + 2 * v._2))
+        }
+      }
+
+      column.close
+    }}
+  }
+
   test("Int Apis") {
     (MemoryMode.ON_HEAP :: MemoryMode.OFF_HEAP :: Nil).foreach { memMode => {
       val seed = System.currentTimeMillis()