Add full TD0 export support with encoding/decoding

Implemented TD0 (Teledisk) image export, supporting all sector data formats: raw, repeated 2-byte pattern, and RLE. Added BytePattern and RLE modules for encoding/decoding. Refactored TD0 structures and classes for easier serialization and CRC handling. Improved code clarity with named enums and settable encoding methods. Application can now generate valid TD0 disk images.

Author: Digitoxin1

DiskImageTool/DiskImageTool.vbproj

@@ -197,6 +197,7 @@
     <Compile Include="Forms\ImagePreview.vb">
       <SubType>Form</SubType>
     </Compile>
+    <Compile Include="ImageFormats\TD0\TD0BytePattern.vb" />
     <Compile Include="ImageFormats\TD0\TD0Comment.vb" />
     <Compile Include="ImageFormats\TD0\TD0Crc16.vb" />
     <Compile Include="ImageFormats\TD0\TD0Enums.vb" />
@@ -206,6 +207,7 @@
     <Compile Include="ImageFormats\TD0\TD0Loader.vb" />
     <Compile Include="ImageFormats\TD0\TD0Lzhuf.vb" />
     <Compile Include="ImageFormats\TD0\TD0Lzw.vb" />
+    <Compile Include="ImageFormats\TD0\TD0Rle.vb" />
     <Compile Include="ImageFormats\TD0\TD0Sector.vb" />
     <Compile Include="ImageFormats\TD0\TD0SectorDataHeader.vb" />
     <Compile Include="ImageFormats\TD0\TD0SectorHeader.vb" />

DiskImageTool/ImageFormats/TD0/TD0BytePattern.vb

@@ -0,0 +1,84 @@
+Namespace ImageFormats.TD0
+    Module TD0BytePattern
+        Friend Function BytePatternCanEncode(data As Byte()) As Boolean
+            If data Is Nothing OrElse data.Length < 2 Then
+                Return False
+            End If
+
+            Dim p0 As Byte = data(0)
+            Dim p1 As Byte = data(1)
+
+            Dim i As Integer = 0
+            Dim n As Integer = data.Length
+
+            ' Check full 2-byte pairs
+            While i + 1 < n
+                If data(i) <> p0 OrElse data(i + 1) <> p1 Then
+                    Return False
+                End If
+                i += 2
+            End While
+
+            ' Optional odd trailing byte (rare for TD0, but allowed)
+            If i < n Then
+                If data(i) <> p0 Then Return False
+            End If
+
+            Return True
+        End Function
+
+        Friend Function BytePatternDecode(src As Byte(),
+                                                  srcOffset As Integer,
+                                          decodedLength As Integer,
+                                          payloadBytes As Integer) As (Result As Boolean, Data As Byte(), BytesConsumed As Integer, BytesWritten As Integer)
+
+            If src Is Nothing OrElse decodedLength < 0 OrElse payloadBytes < 0 OrElse srcOffset < 0 OrElse srcOffset > src.Length Then
+                Return (False, Nothing, 0, 0)
+            End If
+
+            Dim dst(decodedLength - 1) As Byte
+
+            Dim srcEnd As Integer = Math.Min(src.Length, srcOffset + payloadBytes)
+            Dim s As Integer = srcOffset
+            Dim d As Integer = 0
+
+            While d < decodedLength AndAlso (s + 4) <= srcEnd
+                Dim countWords As Integer = ReadUInt16LE(src, s)
+                Dim p0 As Byte = src(s + 2)
+                Dim p1 As Byte = src(s + 3)
+                s += 4
+
+                If countWords <= 0 Then Exit While
+
+                Dim bytesToWrite As Integer = countWords * 2
+                Dim remaining As Integer = decodedLength - d
+                If bytesToWrite > remaining Then bytesToWrite = remaining
+
+                Dim pairs As Integer = bytesToWrite \ 2
+                For i As Integer = 0 To pairs - 1
+                    dst(d) = p0 : d += 1
+                    dst(d) = p1 : d += 1
+                Next
+
+                ' odd tail (kept to match your original safety behavior)
+                If (bytesToWrite And 1) <> 0 Then
+                    dst(d) = p0
+                    d += 1
+                End If
+            End While
+
+            Return (True, dst, s - srcOffset, d)
+        End Function
+        Friend Function BytePatternEncode(data As Byte()) As Byte()
+            Dim countWords As Integer = data.Length \ 2
+
+            Dim out(3) As Byte
+            WriteUInt16LE(out, 0, countWords)
+            out(2) = data(0)
+            out(3) = data(1)
+
+            Return out
+        End Function
+
+    End Module
+End Namespace

DiskImageTool/ImageFormats/TD0/TD0Comment.vb

@@ -3,10 +3,23 @@
 Namespace ImageFormats.TD0
     Public NotInheritable Class TD0Comment
         Public Const HEADER_LENGTH As Integer = 10
+        Private Const CRC_START As Integer = Offset.DataLength
+        Private Const CRC_END As Integer = Offset.Second
 
         Private ReadOnly _data As Byte()
         Private ReadOnly _header As Byte()
 
+        Private Enum Offset As Integer
+            Crc16 = 0
+            DataLength = 2
+            Year = 4
+            Month0 = 5
+            Day = 6
+            Hour = 7
+            Minute = 8
+            Second = 9
+        End Enum
+
         Public Sub New(imagebuf As Byte(), offset As Integer)
             _header = New Byte(HEADER_LENGTH - 1) {}
             _data = Array.Empty(Of Byte)()
@@ -35,33 +48,44 @@ Namespace ImageFormats.TD0
             End If
         End Sub
 
+        Public Function GetBytes() As Byte()
+            Dim totalLen As Integer = TotalLength
+            Dim buf(totalLen - 1) As Byte
+            ' header
+            Array.Copy(_header, 0, buf, 0, HEADER_LENGTH)
+            ' data
+            Array.Copy(_data, 0, buf, HEADER_LENGTH, _data.Length)
+
+            Return buf
+        End Function
+
         Public ReadOnly Property DataLength As Integer
             Get
-                Return ReadUInt16LE(_header, 2)
+                Return ReadUInt16LE(_header, Offset.DataLength)
             End Get
         End Property
 
         Public ReadOnly Property Day As Integer
             Get
-                Return _header(6)
+                Return _header(Offset.Day)
             End Get
         End Property
 
         Public ReadOnly Property Hour As Integer
             Get
-                Return _header(7)
+                Return _header(Offset.Hour)
             End Get
         End Property
 
         Public ReadOnly Property Minute As Integer
             Get
-                Return _header(8)
+                Return _header(Offset.Minute)
             End Get
         End Property
 
         Public ReadOnly Property Month As Integer
             Get
-                Return _header(5) + 1
+                Return _header(Offset.Month0) + 1
             End Get
         End Property
 
@@ -73,13 +97,13 @@ Namespace ImageFormats.TD0
 
         Public ReadOnly Property Second As Integer
             Get
-                Return _header(9)
+                Return _header(Offset.Second)
             End Get
         End Property
 
         Public ReadOnly Property StoredCrc16 As UShort
             Get
-                Return ReadUInt16LE(_header, 0)
+                Return ReadUInt16LE(_header, Offset.Crc16)
             End Get
         End Property
 
@@ -102,7 +126,7 @@ Namespace ImageFormats.TD0
         Public ReadOnly Property Year As Integer
             Get
                 ' year since 1900
-                Return 1900 + _header(4)
+                Return 1900 + _header(Offset.Year)
             End Get
         End Property
 
@@ -113,8 +137,7 @@ Namespace ImageFormats.TD0
         Public Function ComputedCrc16() As UShort
             Dim crc As UShort = 0US
 
-            ' header bytes [2..9]
-            For i = 2 To 9
+            For i = CRC_START To CRC_END
                 crc = TD0Crc16.Update(crc, _header(i))
             Next
 

DiskImageTool/ImageFormats/TD0/TD0Enums.vb

@@ -16,10 +16,20 @@
         Rle = 2
     End Enum
 
-    Friend Module TD0Constants
+    Friend Module TD0Helpers
         Friend Const TD0_MAX_BUFSZ As Integer = 1024 * 1024 * 4 ' 4 MiB
         Friend Function ReadUInt16LE(buf As Byte(), offset As Integer) As Integer
             Return CInt(buf(offset)) Or (CInt(buf(offset + 1)) << 8)
         End Function
+
+        Friend Sub WriteUInt16LE(buf As Byte(), offset As Integer, value As UShort)
+            buf(offset) = CByte(value And &HFFUS)
+            buf(offset + 1) = CByte((value >> 8) And &HFFUS)
+        End Sub
+
+        Friend Sub WriteUInt16LE(buf As Byte(), offset As Integer, value As Integer)
+            buf(offset) = CByte(value And &HFF)
+            buf(offset + 1) = CByte((value >> 8) And &HFF)
+        End Sub
     End Module
 End Namespace