Fast Search CoboBox and ListBox using Windows API

Option Explicit
Public Sub FindIndexStr(ctlSource As Control, _
  ByVal str As String, intKey As Integer, _
  Optional ctlTarget As Variant)
Dim lngIdx As Long
Dim FindString As String
If (intKey < 32 Or intKey > 127) And _
  (Not (intKey = 13 Or intKey = 8)) Then Exit Sub
If Not intKey = 13 Or intKey = 8 Then
  If Len(ctlSource.Text) = 0 Then
    FindString = str & Chr$(intKey)
  Else
    FindString = Left$(str, ctlSource.SelStart) & Chr$(intKey)
  End If
End If
If intKey = 8 Then
  If Len(ctlSource.Text) = 0 Then Exit Sub
  Dim numChars As Integer
  numChars = ctlSource.SelStart - 1
  'FindString = Left(str, numChars)
  If numChars > 0 Then FindString = Left(str, numChars)
End If
If IsMissing(ctlTarget) And TypeName(ctlSource) = "ComboBox" Then
  Set ctlTarget = ctlSource
    If intKey = 13 Then
     Call SendMessageStr(ctlTarget.hWnd, _
       CB_SHOWDROPDOWN, True, 0&)
     Exit Sub
    End If
  lngIdx = SendMessageStr(ctlTarget.hWnd, _
    CB_FINDSTRING, -1, FindString)
ElseIf TypeName(ctlTarget) = "ListBox" Then
  If intKey = 13 Then Exit Sub '???
  lngIdx = SendMessageStr(ctlTarget.hWnd, _
    LB_FINDSTRING, -1, FindString)
Else
  Exit Sub
End If
 
If lngIdx <> -1 Then
    ctlTarget.ListIndex = lngIdx
    If TypeName(ctlSource) = "TextBox" Then ctlSource.Text = ctlTarget.List(lngIdx)
    ctlSource.SelStart = Len(FindString)
    ctlSource.SelLength = Len(ctlSource.Text) - ctlSource.SelStart
End If
intKey = 0
End Sub