Find Good Multiplier

Sub FindGoodMultiplier( _
  ByVal Modulus As Long, _
  Optional ByVal OverflowAt As Long = 32767)

  Dim Multiplier As Long
  Dim Hit() As Boolean
  Dim m As Long
  Dim x As Long
  Dim i As Long

  Do While Modulus > 1
    ReDim Hit(1 To Modulus - 1) As Boolean
    m = OverflowAt \ Modulus
    If m >= Int(Modulus ^ (2 / 3)) Then m = Int(Modulus ^ (2 / 3))
    For Multiplier = m To 2 Step -1
      For i = 1 To Modulus - 1: Hit(i) = False: Next i
      x = 1
      For i = 2 To Modulus - 1
        If x = 0 Then Exit For
        If Hit(x) Then Exit For
        Hit(x) = True
        x = (x * Multiplier) Mod Modulus
      Next i
      If i > Modulus - 1 Then
        Debug.Print Multiplier & " is a good multiplier for modulus " & Modulus
        Exit Sub
      End If
    Next Multiplier
    Modulus = Modulus - 1
    DoEvents
  Loop

  Debug.Print "No good multiplier was found"

End Sub

' 1020 is a good multiplier for modulus 32749
' 63 is a good multiplier for modulus 509
' 21 is a good multiplier for modulus 97
' 23 is a good multiplier for modulus 127