Scala merge sort implementation

mergeSort.scala

import scala.annotation.tailrec

object sortings {
  
 //p <= q < r
  def merge(ar: Array[Int], p: Int, q: Int, r: Int): Array[Int] = {
    val x    = q - p + 1
    val left = new Array[Int](x + 1)
    Array.copy(ar, p, left, 0, x)
    left(left.length - 1) = Int.MaxValue
    val y     = r - q
    val right = new Array[Int](y + 1)
    Array.copy(ar, q + 1, right, 0, y)
    right(right.length - 1) = Int.MaxValue
    @tailrec
    def loop(i: Int, li: Int, ri: Int): Unit =
      if (i > r) Unit
      else {
        if (left(li) <= right(ri)) {
          ar(i) = left(li)
          loop(i + 1, li + 1, ri)
        } else {
          ar(i) = right(ri)
          loop(i + 1, li, ri + 1)
        }
      }
    loop(p, 0, 0)
    ar
  }

  def mergeSort(ar: Array[Int]): Array[Int] = {
    def mergeSortLoop(ar: Array[Int], p: Int, r: Int): Unit = {
      if (p >= r) Unit
      else {
        val q = (p + r) / 2
        mergeSortLoop(ar, p, q)
        mergeSortLoop(ar, q + 1, r)
        merge(ar, p, q, r)
      }
    }
    mergeSortLoop(ar, 0, ar.length - 1)
    ar
  }
  
}