[SPARK-48596][SQL] Perf improvement for calculating hex string for long

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala

@@ -1018,9 +1018,9 @@ case class Bin(child: Expression)
 }
 
 object Hex {
-  val hexDigits = Array[Char](
-    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
-  ).map(_.toByte)
+  private final val hexDigits =
+    Array[Byte]('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F')
+  private final val ZERO_UTF8 = UTF8String.fromBytes(Array[Byte]('0'))
 
   // lookup table to translate '0' -> 0 ... 'F'/'f' -> 15
   val unhexDigits = {
@@ -1036,24 +1036,26 @@ object Hex {
     val value = new Array[Byte](length * 2)
     var i = 0
     while (i < length) {
-      value(i * 2) = Hex.hexDigits((bytes(i) & 0xF0) >> 4)
-      value(i * 2 + 1) = Hex.hexDigits(bytes(i) & 0x0F)
+      value(i * 2) = hexDigits((bytes(i) & 0xF0) >> 4)
+      value(i * 2 + 1) = hexDigits(bytes(i) & 0x0F)
       i += 1
     }
     UTF8String.fromBytes(value)
   }
 
   def hex(num: Long): UTF8String = {
-    // Extract the hex digits of num into value[] from right to left
-    val value = new Array[Byte](16)
+    val zeros = jl.Long.numberOfLeadingZeros(num)
+    if (zeros == jl.Long.SIZE) return ZERO_UTF8
+    val len = (jl.Long.SIZE - zeros + 3) / 4
     var numBuf = num
-    var len = 0
-    do {
-      len += 1
-      value(value.length - len) = Hex.hexDigits((numBuf & 0xF).toInt)
+    val value = new Array[Byte](len)
+    var i = len - 1
+    while (i >= 0) {
+      value(i) = hexDigits((numBuf & 0xF).asInstanceOf[Int])
       numBuf >>>= 4
-    } while (numBuf != 0)
-    UTF8String.fromBytes(java.util.Arrays.copyOfRange(value, value.length - len, value.length))
+      i -= 1
+    }
+    UTF8String.fromBytes(value)
   }
 
   def unhex(bytes: Array[Byte]): Array[Byte] = {

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/HexSuite.scala

@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.expressions
+
+import org.apache.spark.SparkFunSuite
+
+class HexSuite extends SparkFunSuite {
+  test("SPARK-48596: hex long values") {
+    assert(Hex.hex(0).toString === "0")
+    assert(Hex.hex(1).toString === "1")
+    assert(Hex.hex(15).toString === "F")
+    assert(Hex.hex(16).toString === "10")
+    assert(Hex.hex(255).toString === "FF")
+    assert(Hex.hex(256).toString === "100")
+    assert(Hex.hex(4095).toString === "FFF")
+    assert(Hex.hex(4096).toString === "1000")
+    assert(Hex.hex(65535).toString === "FFFF")
+    assert(Hex.hex(65536).toString === "10000")
+    assert(Hex.hex(1048575).toString === "FFFFF")
+    assert(Hex.hex(1048576).toString === "100000")
+    assert(Hex.hex(-1).toString === "FFFFFFFFFFFFFFFF")
+    assert(Hex.hex(Long.MinValue).toString === "8000000000000000")
+    assert(Hex.hex(Long.MaxValue).toString === "7FFFFFFFFFFFFFFF")
+  }
+}