Github user davies commented on a diff in the pull request:
https://github.com/apache/spark/pull/7113#discussion_r33689791
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala
---
@@ -354,6 +354,67 @@ case class Pow(left: Expression, right: Expression)
}
}
+/**
+ * Performs the inverse operation of HEX.
+ * Resulting characters are returned as a byte array.
+ */
+case class UnHex(child: Expression) extends UnaryExpression with
Serializable {
+
+ override def dataType: DataType = BinaryType
+
+ override def checkInputDataTypes(): TypeCheckResult = {
+ if (child.dataType.isInstanceOf[StringType] || child.dataType ==
NullType) {
+ TypeCheckResult.TypeCheckSuccess
+ } else {
+ TypeCheckResult.TypeCheckFailure(s"unHex accepts String type, not
${child.dataType}")
+ }
+ }
+
+ override def eval(input: InternalRow): Any = {
+ val num = child.eval(input)
+ if (num == null) {
+ null
+ } else {
+ unhex(num.asInstanceOf[UTF8String].getBytes)
+ }
+ }
+
+ private val hexDigits = {
+ val array = Array.fill[Byte](128)(-1)
+ (0 to 9).foreach(i => array('0' + i) = i.toByte)
+ (0 to 5).foreach(i => array('A' + i) = (i + 10).toByte)
+ (0 to 5).foreach(i => array('a' + i) = (i + 10).toByte)
+ array
+ }
+
+ private def toDigit(b: Byte): Byte = {
+ val digit = hexDigits(b)
+ if (digit == -1) {
+ throw new NumberFormatException(s"invalid hex number $b")
+ }
+ digit
+ }
+
+ private def unhex(inputBytes: Array[Byte]): Array[Byte] = {
+ var bytes = inputBytes
+ if ((bytes.length & 0x01) != 0) {
+ bytes = 48.toByte +: bytes // padding with '0'
--- End diff --
I think we can padding with `0` without allocation. you can use `'0'.toByte`
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