Added code to display some info about the IHDR, pHYs, and tEXt chunks.
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@ -24,10 +24,13 @@
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If Not FileIO.FileSystem.FileExists(filename) Then
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Console.WriteLine("File {0} not found!", filename)
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Exit Sub
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End If
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Dim fs As New IO.FileStream(filename, IO.FileMode.Open, IO.FileAccess.Read, IO.FileShare.Read)
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Dim fi As New IO.FileInfo(filename)
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Dim sizedigits As Integer = Math.Ceiling(Math.Log10(fs.Length))
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While Not fs.Position = fs.Length
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Dim startposition As Long = fs.Position
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FindHeader(fs)
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@ -59,40 +62,54 @@
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End If
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Dim buf() As Byte
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Dim lenbuf(3), nameanddatabuf(), databuf(), crcbuf(3) As Byte
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Dim len As Integer
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Dim chunklength As UInt32
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Dim chunktype As String = String.Empty
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While chunktype <> "IEND" AndAlso fs.Position <> fs.Length
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ReDim buf(3)
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len = fs.Read(buf, 0, 4)
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Console.ForegroundColor = ConsoleColor.White
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'read chunk length
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len = fs.Read(lenbuf, 0, 4)
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If len <> 4 Then
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Console.WriteLine("Incomplete chunk length header")
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Exit While
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End If
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'big endian
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chunklength = &H1000000L * buf(0) + &H10000L * buf(1) + &H100L * buf(2) + buf(3)
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Console.Write("{0,10}:", chunklength)
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'read and print chunk length and offset in the file
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chunklength = BigEndianUInt32(lenbuf)
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Console.Write("{0," & sizedigits & "} @ {1,-" & sizedigits & "}:", chunklength, fs.Position - 4)
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ReDim buf(chunklength + 3)
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len = fs.Read(buf, 0, chunklength + 4)
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'read in the chunk data and type
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ReDim nameanddatabuf(chunklength + 3)
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ReDim databuf(chunklength - 1)
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len = fs.Read(nameanddatabuf, 0, chunklength + 4)
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'rewind and read only the chunk data
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fs.Seek(-chunklength, IO.SeekOrigin.Current)
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fs.Read(databuf, 0, chunklength)
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'check for incomplete reads
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If len <> chunklength + 4 Then
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Console.WriteLine("Incomplete chunk data")
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Exit While
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End If
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chunktype = System.Text.Encoding.ASCII.GetString(buf, 0, 4)
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Console.Write(chunktype & " ")
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Dim datachecksum As UInt32 = Crc32.ComputeChecksum(buf)
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ReDim buf(3)
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len = fs.Read(buf, 0, 4)
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'get chunk type as string
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chunktype = System.Text.Encoding.ASCII.GetString(nameanddatabuf, 0, 4)
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Console.Write(chunktype & " ")
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'compute checksum of the chunk
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Dim datachecksum As UInt32 = Crc32.ComputeChecksum(nameanddatabuf)
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'read reported checksum and compare it to the file
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len = fs.Read(crcbuf, 0, 4)
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If len <> 4 Then
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Console.WriteLine("Incomplete CRC data")
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End If
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Dim chunkchecksum As UInt32 = &H1000000L * buf(0) + &H10000L * buf(1) + &H100L * buf(2) + buf(3)
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Dim chunkchecksum As UInt32 = BigEndianUInt32(crcbuf)
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If chunkchecksum = datachecksum Then
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Console.Write("ok")
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Else
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@ -100,6 +117,10 @@
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End If
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Console.WriteLine()
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'print info for some chunks
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Console.ForegroundColor = ConsoleColor.Gray
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PrintChunkInfo(chunktype, databuf)
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End While
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If extract Then
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@ -110,6 +131,10 @@
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End While
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fs.Close()
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#If CONFIG = "Debug" Then
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Console.ReadKey()
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#End If
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End Sub
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Public Sub FindHeader(fs As IO.FileStream)
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@ -128,6 +153,10 @@
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End While
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End Sub
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Private Function BigEndianUInt32(ByRef buf As Byte(), Optional offset As Integer = 0) As UInt32
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Return &H1000000L * buf(0 + offset) + &H10000L * buf(1 + offset) + &H100L * buf(2 + offset) + buf(3 + offset)
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End Function
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Public Sub CopyPart(srcfile As String, destfile As String, offset As Long, bytes As Long)
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Dim srcfs As New IO.FileStream(srcfile, IO.FileMode.Open, IO.FileAccess.Read, IO.FileShare.Read)
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Dim destfs As New IO.FileStream(destfile, IO.FileMode.Create, IO.FileAccess.Write, IO.FileShare.Read)
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@ -139,6 +168,110 @@
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destfs.Close()
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End Sub
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Private Sub PrintChunkInfo(chunktype As String, ByRef data As Byte())
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Select Case chunktype
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Case "IHDR"
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'image width
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Console.WriteLine("width: {0} px", BigEndianUInt32(data, 0))
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'image height
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Console.WriteLine("height: {0} px", BigEndianUInt32(data, 4))
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'bit depth
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Dim bitdepth As Byte = data(8)
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If {1, 2, 4, 8, 16}.Contains(bitdepth) Then
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Console.WriteLine("bit depth: {0} bits/sample", bitdepth)
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Else
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Console.WriteLine("bit depth: {0} bits/sample INVALID", bitdepth)
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End If
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'color types
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Dim colortype As Byte = data(9)
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Dim colortypename As String
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Select Case colortype
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Case 0
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colortypename = "greyscale"
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If Not {1, 2, 4, 8, 16}.Contains(bitdepth) Then
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colortypename &= ", INVALID BIT DEPTH"
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End If
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Case 2
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colortypename = "truecolor"
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If Not {8, 16}.Contains(bitdepth) Then
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colortypename &= ", INVALID BIT DEPTH"
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End If
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Case 3
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colortypename = "indexed"
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If Not {1, 2, 4, 8}.Contains(bitdepth) Then
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colortypename &= ", INVALID BIT DEPTH"
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End If
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Case 4
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colortypename = "greyscale with alpha"
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If Not {8, 16}.Contains(bitdepth) Then
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colortypename &= ", INVALID BIT DEPTH"
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End If
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Case 6
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colortypename = "truecolor with alpha"
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If Not {8, 16}.Contains(bitdepth) Then
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colortypename &= ", INVALID BIT DEPTH"
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End If
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Case Else
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colortypename = "UNKNOWN"
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End Select
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Console.WriteLine("color type: {0} ({1})", colortype, colortypename)
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'compression method
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If data(10) = 0 Then
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Console.WriteLine("compression method: 0 (deflate)")
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Else
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Console.WriteLine("compression method: {0} (UNKNOWN)", data(10))
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End If
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'filter method
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If data(11) = 0 Then
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Console.WriteLine("filter method: 0 (adaptive)")
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Else
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Console.WriteLine("filter method: {0} (UNKNOWN)", data(11))
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End If
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'interlace method
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If data(12) = 0 Then
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Console.WriteLine("interlace method: 0 (no interlace)")
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ElseIf data(12) = 1 Then
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Console.WriteLine("interlace method: 1 (Adam7)")
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Else
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Console.WriteLine("interlace method: {0} (UNKNOWN)", data(12))
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End If
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'end IHDR
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Case "pHYs"
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Dim unitsaremetres As Boolean = (data(8) = 1)
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If unitsaremetres Then
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Console.WriteLine("pixels per unit, x: {0} px ({1:g} ppi)", BigEndianUInt32(data, 0), BigEndianUInt32(data, 0) * 0.0254)
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Console.WriteLine("pixels per unit, y: {0} px ({1:g} ppi)", BigEndianUInt32(data, 4), BigEndianUInt32(data, 0) * 0.0254)
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Else
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Console.WriteLine("pixels per unit, x: {0} px", BigEndianUInt32(data, 0))
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Console.WriteLine("pixels per unit, y: {0} px", BigEndianUInt32(data, 4))
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End If
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If data(8) = 0 Then
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Console.WriteLine("units: 0 (unknown)")
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ElseIf data(8) = 1 Then
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Console.WriteLine("units: 1 (metre)")
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Else
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Console.WriteLine("units: {0} (UNKNOWN)", data(8))
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End If
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Case "tEXt"
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Dim keywordlength As Integer = Array.FindIndex(data, Function(x) x = &H0) - 1
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Dim keyword(keywordlength - 1) As Byte
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Dim textstring(data.Length - keywordlength - 1 - 1) As Byte
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Array.Copy(data, 0, keyword, 0, keywordlength)
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Array.Copy(data, keywordlength + 1, textstring, 0, data.Length - keywordlength - 1)
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Console.WriteLine("keyword: {0}", System.Text.Encoding.GetEncoding("ISO-8859-1").GetString(keyword))
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Console.WriteLine("value: {0}", System.Text.Encoding.GetEncoding("ISO-8859-1").GetString(textstring))
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End Select
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End Sub
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Public Class Crc32
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Shared table As UInteger()
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