Data commit

Task/Base64-decode-data/QB64/base64-decode-data.qb64

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+Option _Explicit
+
+Dim As String udata, decoded
+udata = "VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLVBhdWwgUi5FaHJsaWNo"
+
+decoded = decode(udata)
+
+Print udata
+Print decoded
+
+Function findIndex& (value As _Unsigned _Byte)
+    If Asc("A") <= value And value <= Asc("Z") Then
+        findIndex = value - Asc("A")
+        Exit Function
+    End If
+    If Asc("a") <= value And value <= Asc("z") Then
+        findIndex = value - Asc("a") + 26
+        Exit Function
+    End If
+    If Asc("0") <= value And value <= Asc("9") Then
+        findIndex = value - Asc("0") + 52
+        Exit Function
+    End If
+    If value = Asc("+") Then
+        findIndex = 62
+        Exit Function
+    End If
+    If value = Asc("/") Then
+        findIndex = 63
+        Exit Function
+    End If
+    findIndex = -1
+End Function
+
+Function encode$ (source As String)
+    Dim As String Base64: Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+    Dim As _Unsigned _Integer64 length: length = Len(source)
+    Dim As _Unsigned _Integer64 it, strend
+    Dim As Long acc
+    Dim As String sink
+    strend = length
+    While it <> strend
+        Dim As _Unsigned _Byte b1, b2, b3, b4
+        it = it + 1
+        b1 = Asc(Mid$(source, it, 1))
+        sink = sink + Mid$(Base64, _SHR(b1, 2), 1)
+        acc = _SHL(b1 And &H3, 4)
+        If it <> strend Then
+            it = it + 1
+            b2 = Asc(Mid$(source, it, 1))
+            acc = acc Or _SHR(b2, 4)
+            sink = sink + Mid$(Base64, acc, 1)
+            acc = _SHL(b2 And &HF, 2)
+            If it <> strend Then
+                it = it + 1
+                b3 = Asc(Mid$(source, it, 1))
+                acc = acc Or _SHR(b3, 6)
+                sink = sink + Mid$(Base64, acc, 1)
+                sink = sink + Mid$(Base64, b3 And &H3F, 1)
+            Else
+                sink = sink + Mid$(Base64, acc, 1)
+                sink = sink + "="
+            End If
+        Else
+            sink = sink + Mid$(Base64, acc, 1)
+            sink = sink + "="
+            sink = sink + "="
+        End If
+    Wend
+    encode = sink
+End Function
+
+Function decode$ (source As String)
+    Dim As _Unsigned _Integer64 length: length = Len(source)
+    Dim As _Unsigned _Integer64 it, strend
+    Dim As Long acc
+    Dim As String sink
+    strend = length
+    While it <> strend
+        Dim As _Unsigned _Byte b1, b2, b3, b4
+        it = it + 1
+        b1 = Asc(Mid$(source, it, 1))
+        it = it + 1
+        b2 = Asc(Mid$(source, it, 1))
+        it = it + 1
+        b3 = Asc(Mid$(source, it, 1))
+        it = it + 1
+        b4 = Asc(Mid$(source, it, 1))
+        Dim As Long i1, i2
+        i1 = findIndex(b1)
+        i2 = findIndex(b2)
+        acc = _SHL(i1, 2)
+        acc = acc Or _SHR(i2, 4)
+        sink = sink + Chr$(acc)
+        If b3 <> Asc("=") Then
+            Dim As Long i3
+            i3 = findIndex(b3)
+            acc = _SHL(i2 And &HF, 4)
+            acc = acc Or _SHR(i3, 2)
+            sink = sink + Chr$(acc)
+            If b4 <> Asc("=") Then
+                Dim As Long i4
+                i4 = findIndex(b4)
+                acc = _SHL(i3 And &H3, 6)
+                acc = acc Or i4
+                sink = sink + Chr$(acc)
+            End If
+        End If
+    Wend
+    decode = sink
+End Function