Speed up Loop VBA

[PcMax]

Hi,

I have a column with numeric data and a function of a search for unique data would assign the position.
The code should work with 200,000 rows and 20,000 different values (all listed)

Unique list:
123.20
11.40
34.00
12.10

Column G
123.20
11.40
123.20
34.00
11.40
12.10
---------------
Unique list:
123.20 |1
11.40 |2
123.20 |1
34.00 |3
11.40 |2
12.10 |4

I attach an example to improve.

Sub Add_Value()
    Dim row As Long, descr As String
    Application.ScreenUpdating = False
    row = 2
    Do While Cells(row, "G").Value <> ""
        Select Case Cells(row, "G").Value
            Case 123.20: descr = 1
            Case 11.40: descr = 2
            Case 34.00: descr = 3
            Case 12.10: descr = 4
            'Ecc...
'            Case Else: descr = ""
        End Select
        Cells(row, "H").Value = descr
        row = row + 1
    Loop
    Application.ScreenUpdating = True
    
End Sub