Преобразуйте массив перестановкой столбцов: первое с последним, второй с предпоследним - Visual Basic .NET

Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
    Dim ii As Integer = 6
    Dim jj As Integer = 5
    Dim M(,) As Integer = createMatrix(ii, jj, -15, 5)
    swapCol(0, 5, M)
    swapCol(1, 4, M)
    swapCol(2, 3, M)
End Sub
Private Function createMatrix(ByVal r As Integer, ByVal c As Integer, ByVal t1 As Integer, ByVal t2 As Integer) As Integer(,)
    Dim randi As New Random
    Dim mm(r, c) As Integer
    For i = 0 To r
        For j = 0 To c
            mm(i, j) = randi.Next(t1, t2 + 1)
        Next
    Next
    Return mm
End Function
Private Sub swapCol(ByVal j1 As Integer, ByVal j2 As Integer, ByVal mm(,) As Integer)
    For i = 0 To mm.GetUpperBound(0)
        swap(mm(i, j1), mm(i, j2))
    Next
End Sub
Private Sub swap(ByRef v1 As Integer, ByRef v2 As Integer)
    v1 = v1 Xor v2
    v2 = v1 Xor v2
    v1 = v1 Xor v2
End Sub