B4R Code Snippet Base64 decoding

Erel

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B4X:
Sub Process_Globals
   Public Serial1 As Serial
End Sub

Private Sub AppStart
   Serial1.Initialize(115200)
   Log("AppStart")
   Dim Result(100) As Byte
   Dim length As UInt = DecodeBase64(Result, "RGVjb2RpbmcgQmFzZTY0IHN0cmluZyB3aXRoIEI0UiEhIQ==")
   Dim bc As ByteConverter 'rRandomAccessFile library
   Log(bc.SubString2(Result, 0, length))
End Sub

'Returns the length of the decoded data
Sub DecodeBase64(Result() As Byte, Text() As Byte) As UInt
   Dim rawlength As Int
   For i = 0 To Text.Length - 1
       Dim u As Byte = Text(i)
       If u >= 43 And u <> 61 Then rawlength = rawlength + 1
   Next
   Dim length As Int = Min(Result.Length, rawlength * 3 / 4)
   Dim si = -1, ri = 0 As Int
   Do While ri < length
       Dim four(4) As Byte
       For i = 0 To 3
           si = si + 1
           Do While Text(si) < 43
               si = si + 1
           Loop
           four(i) = GetBase64Index(Text(si))
       Next
       Result(ri) = Bit.ShiftLeft(four(0), 2) + Bit.ShiftRight(four(1), 4)
       If ri + 1 = length Then Exit
       Result(ri + 1) = Bit.ShiftLeft(four(1), 4) + Bit.ShiftRight(four(2), 2)
       If ri + 2 = length Then Exit
       Result(ri + 2) = Bit.ShiftLeft(four(2), 6) + Bit.ShiftRight(four(3), 0)
       ri = ri + 3
   Loop
   Return length
End Sub

Sub GetBase64Index(u As Int) As Int
   If u = 43 Then Return 63
   If u = 47 Then Return 63
   If u = 61 Then Return 0
   If u <= 57 Then Return u - 48 + 52
   If u <= 90 Then Return u - 65
   If u <= 122 Then Return u - 97 + 26
   Log("Error: ", u)
   Return 0
End Sub
As demonstrated above the result is stored in the Result array and the length is returned.
 
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