qb64-include/btoa.bm

$if btoa = undefined then
$let btoa = defined
Function btoa$ (strng As String)
    Const B64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
    Dim c1 As _Unsigned _Byte
    Dim c2 As _Unsigned _Byte
    Dim c3 As _Unsigned _Byte
    Dim t1 As _Unsigned _Byte
    Dim t2 As _Unsigned _Byte
    Dim t3 As _Unsigned _Byte
    Dim t4 As _Unsigned _Byte
    Dim i As Long
    Dim Buffer As String

    For i = 1 To Len(strng) Step 3
        c1 = Asc(Mid$(strng, i, 1))
        t1 = _SHR((c1), 2)
        Buffer = Buffer + Mid$(B64, t1 + 1, 1)
        If Len(strng) >= i + 1 Then
            c2 = Asc(Mid$(strng, i + 1, 1))
            t2 = (_SHL((c1 And &B00000011), 4)) Or (_SHR((c2), 4))
            Buffer = Buffer + Mid$(B64, t2 + 1, 1)
        Else
            t2 = (_SHL((c1 And &B00000011), 4))
            Buffer = Buffer + Mid$(B64, t2 + 1, 1)
            Buffer = Buffer + "=="
            btoa$ = Buffer
            Exit Function
        End If
        If Len(strng) >= i + 2 Then
            c3 = Asc(Mid$(strng, i + 2, 1))
            t3 = (_SHL((c2 And &B00001111), 2)) Or (_SHR((c3), 6))
            Buffer = Buffer + Mid$(B64, t3 + 1, 1)
            t4 = c3 And &B00111111
            Buffer = Buffer + Mid$(B64, t4 + 1, 1)
        Else
            t3 = (_SHL((c2 And &B00001111), 2))
            Buffer = Buffer + Mid$(B64, t3 + 1, 1)
            Buffer = Buffer + "="
            btoa$ = Buffer
            Exit Function
        End If
    Next
    btoa$ = Buffer
End Function
$end if