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compression.cs
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compression.cs
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using System;
using System.Diagnostics.Contracts;
using System.IO;
using System.Linq;
using System.Collections.Generic;
using System.Collections;
using System.Diagnostics;
using System.Text;
namespace Kavod.Vba.Compression
{
/// <summary>
/// A CompressedChunk is a record that encodes all data from a DecompressedChunk (section
/// 2.4.1.1.3) in compressed format. A CompressedChunk has two parts: a CompressedChunkHeader
/// (section 2.4.1.1.5) followed by a CompressedChunkData (section 2.4.1.1.6). The number of bytes
/// in a CompressedChunk MUST be greater than or equal to 3. The number of bytes in a
/// CompressedChunk MUST be less than or equal to 4098.
/// </summary>
/// <remarks></remarks>
internal class CompressedChunk
{
internal CompressedChunk(DecompressedChunk decompressedChunk)
{
// Contract.Requires<ArgumentNullException>(decompressedChunk != null);
// Contract.Ensures(Header != null);
// Contract.Ensures(ChunkData != null);
ChunkData = new CompressedChunkData(decompressedChunk);
if (ChunkData.Size >= Globals.MaxBytesPerChunk)
{
ChunkData = new RawChunk(decompressedChunk.Data);
}
Header = new CompressedChunkHeader(ChunkData);
}
internal CompressedChunk(BinaryReader dataReader)
{
// Contract.Requires<ArgumentNullException>(dataReader != null);
// Contract.Ensures(Header != null);
// Contract.Ensures(ChunkData != null);
Header = new CompressedChunkHeader(dataReader);
if (Header.IsCompressed)
{
ChunkData = new CompressedChunkData(dataReader, Header.CompressedChunkDataSize);
}
else
{
ChunkData = new RawChunk(dataReader.ReadBytes(Header.CompressedChunkDataSize));
}
}
internal CompressedChunkHeader Header { get; }
internal IChunkData ChunkData { get; }
internal byte[] SerializeData()
{
var serializedHeader = Header.SerializeData();
var serializedChunkData = ChunkData.SerializeData();
var data = serializedHeader.Concat(serializedChunkData);
if (!Header.IsCompressed)
{
var dataLength = serializedHeader.LongLength + serializedChunkData.LongLength;
var paddingLength = Globals.NumberOfChunkHeaderBytes
+ Globals.MaxBytesPerChunk
- dataLength;
var padding = Enumerable.Repeat(Globals.PaddingByte, (int)paddingLength);
data = data.Concat(padding);
}
return data.ToArray();
}
}
/// <summary>
/// If CompressedChunkHeader.CompressedChunkFlag (section 2.4.1.1.5) is 0b0, CompressedChunkData
/// contains an array of CompressedChunkHeader.CompressedChunkSize elements plus 3 bytes of
/// uncompressed data. If CompressedChunkHeader CompressedChunkFlag is 0b1, CompressedChunkData
/// contains an array of TokenSequence (section 2.4.1.1.7) elements.
/// </summary>
/// <remarks></remarks>
internal class CompressedChunkData : IChunkData
{
private readonly List<TokenSequence> _tokensequences = new List<TokenSequence>();
internal CompressedChunkData(DecompressedChunk chunk)
{
// Contract.Requires<ArgumentNullException>(chunk != null);
var tokens = Tokenizer.TokenizeUncompressedData(chunk.Data);
_tokensequences.AddRange(tokens.ToTokenSequences());
}
internal CompressedChunkData(BinaryReader dataReader, UInt16 compressedChunkDataSize)
{
var data = dataReader.ReadBytes(compressedChunkDataSize);
using (var reader = new BinaryReader(new MemoryStream(data)))
{
var position = 0;
while (reader.BaseStream.Position < reader.BaseStream.Length)
{
var sequence = TokenSequence.GetFromCompressedData(reader, position);
_tokensequences.Add(sequence);
position += (int)sequence.Tokens.Sum(t => t.Length);
}
}
}
internal IEnumerable<TokenSequence> TokenSequences => _tokensequences;
public byte[] SerializeData()
{
// get data from TokenSequences.
var data = from t in _tokensequences
from d in t.SerializeData()
select d;
return data.ToArray();
}
// TODO this is probably really inefficient.
public int Size => SerializeData().Length;
}
internal class CompressedChunkHeader
{
internal CompressedChunkHeader(IChunkData chunkData)
{
IsCompressed = chunkData is CompressedChunkData;
CompressedChunkSize = (ushort) (chunkData.Size + 2);
}
internal CompressedChunkHeader(UInt16 header)
{
DecodeHeader(header);
}
internal CompressedChunkHeader(BinaryReader dataReader)
{
var header = dataReader.ReadUInt16();
DecodeHeader(header);
}
private void DecodeHeader(UInt16 header)
{
var temp = (UInt16)(header & 0xf000);
switch (temp)
{
case 0xb000:
IsCompressed = true;
break;
case 0x3000:
IsCompressed = false;
break;
default:
throw new Exception();
}
// 2.4.1.3.12 Extract CompressedChunkSize
// SET temp TO Header BITWISE AND 0x0FFF
// SET Size TO temp PLUS 3
CompressedChunkSize = (UInt16)((header & 0xfff) + 3);
ValidateChunkSizeAndCompressedFlag();
}
internal bool IsCompressed { get; private set; }
internal UInt16 CompressedChunkSize { get; private set; }
internal UInt16 CompressedChunkDataSize => (UInt16)(CompressedChunkSize - 2);
internal byte[] SerializeData()
{
ValidateChunkSizeAndCompressedFlag();
UInt16 header;
if (IsCompressed)
{
header = (UInt16)(0xb000 | (CompressedChunkSize - 3));
}
else
{
header = (UInt16)(0x3000 | (CompressedChunkSize - 3));
}
return BitConverter.GetBytes(header);
}
private void ValidateChunkSizeAndCompressedFlag()
{
if (IsCompressed
&& CompressedChunkSize > 4098)
{
throw new Exception();
}
if (!IsCompressed
&& CompressedChunkSize != 4098)
{
throw new Exception();
}
}
}
/// <summary>
/// A CompressedContainer is an array of bytes holding the compressed data. The Decompression
/// algorithm (section 2.4.1.3.1) processes a CompressedContainer to populate a DecompressedBuffer.
/// The Compression algorithm (section 2.4.1.3.6) processes a DecompressedBuffer to produce a
/// CompressedContainer. A CompressedContainer MUST be the last array of bytes in a stream (1).
/// On read, the end of stream (1) indicator determines when the entire CompressedContainer has
/// been read. The CompressedContainer is a SignatureByte followed by array of CompressedChunk
/// (section 2.4.1.1.4) structures.
/// </summary>
/// <remarks></remarks>
internal class CompressedContainer
{
private const byte SignatureByteSig = 0x1;
private readonly List<CompressedChunk> _compressedChunks = new List<CompressedChunk>();
internal CompressedContainer(byte[] compressedData)
{
var reader = new BinaryReader(new MemoryStream(compressedData));
if (reader.ReadByte() != SignatureByteSig)
{
throw new Exception();
}
while (reader.BaseStream.Position < reader.BaseStream.Length)
{
_compressedChunks.Add(new CompressedChunk(reader));
}
}
internal CompressedContainer(DecompressedBuffer buffer)
{
foreach (var chunk in buffer.DecompressedChunks)
{
_compressedChunks.Add(new CompressedChunk(chunk));
}
}
internal IEnumerable<CompressedChunk> CompressedChunks => _compressedChunks;
internal byte[] SerializeData()
{
using (var writer = new BinaryWriter(new MemoryStream()))
{
writer.Write(SignatureByteSig);
foreach (var chunk in CompressedChunks)
{
writer.Write(chunk.SerializeData());
}
using (var reader = new BinaryReader(writer.BaseStream))
{
reader.BaseStream.Position = 0;
return reader.ReadBytes((int) reader.BaseStream.Length);
}
}
}
}
/// <summary>
/// CopyToken is a two-byte record interpreted as an unsigned 16-bit integer in little-endian
/// order. A CopyToken is a compressed encoding of an array of bytes from a DecompressedChunk
/// (section 2.4.1.1.3). The byte array encoded by a CopyToken is a byte-for-byte copy of a byte
/// array elsewhere in the same DecompressedChunk, called a CopySequence (section 2.4.1.3.19).
///
/// The starting location, in a DecompressedChunk, is determined by the Compressing a Token
/// (section 2.4.1.3.9) and the Decompressing a Token (section 2.4.1.3.5) algorithms. Packed into
/// the CopyToken is the Offset, the distance, in byte count, to the beginning of the CopySequence.
/// Also packed into the CopyToken is the Length, the number of bytes encoded in the CopyToken.
/// Length also specifies the count of bytes in the CopySequence. The values encoded in Offset and
/// Length are computed by the Matching (section 2.4.1.3.19.4) algorithm.
/// </summary>
/// <remarks></remarks>
internal class CopyToken : IToken, IEquatable<CopyToken>
{
private readonly UInt16 _tokenOffset;
private readonly UInt16 _tokenLength;
/// <summary>
/// Constructor used to create a CopyToken when compressing a DecompressedChunk.
/// </summary>
/// <param name="tokenPosition">
/// The start position of the CopyToken decompressed data in the current DecompressedChunk.
/// </param>
/// <param name="tokenOffset">
/// The offset in bytes from the start position in the current DecompressedChunk from which to
/// start copying.
/// </param>
/// <param name="tokenLength">The number of bytes to copy from the offset.</param>
/// <remarks></remarks>
internal CopyToken(long tokenPosition, UInt16 tokenOffset, UInt16 tokenLength)
{
Position = tokenPosition;
_tokenOffset = tokenOffset;
_tokenLength = tokenLength;
}
/// <summary>
/// Constructor used to create CopyToken instance when reading compressed token from a stream.
/// </summary>
/// <param name="dataReader">
/// A BinaryReader object where the position is located at an encoded CopyToken.
/// </param>
/// <remarks></remarks>
internal CopyToken(BinaryReader dataReader, long position)
{
Position = position;
CopyToken.UnPack(dataReader.ReadUInt16(), Position, out _tokenOffset, out _tokenLength);
}
public long Length => _tokenLength;
internal UInt16 Offset => _tokenOffset;
internal long Position { get; }
internal static UInt16 Pack(long position, UInt16 offset, UInt16 length)
{
// 2.4.1.3.19.3 Pack CopyToken
var result = CopyTokenHelp(position);
if (length > result.MaximumLength)
throw new Exception();
//SET temp1 TO Offset MINUS 1
var temp1 = (UInt16)(offset - 1);
//SET temp2 TO 16 MINUS BitCount
var temp2 = (UInt16)(16 - result.BitCount);
//SET temp3 TO Length MINUS 3
var temp3 = (UInt16)(length - 3);
//SET Token TO (temp1 LEFT SHIFT BY temp2) BITWISE OR temp3
return (UInt16)((temp1 << temp2) | temp3);
}
public void DecompressToken(BinaryWriter writer)
{
// It is possible that the length is greater than the offset which means we would need to
// read more bytes than are available. To handle this we need to read the bytes available
// (ie Offset amount) and then pad the remaining length with copies of the data read from
// the beginning of the buffer.
var streamPosition = writer.BaseStream.Position;
var reader = new BinaryReader(writer.BaseStream, Encoding.Unicode, true);
reader.BaseStream.Position = streamPosition - _tokenOffset;
var copySequence = reader.ReadBytes(Math.Min(_tokenOffset, _tokenLength));
Array.Resize(ref copySequence, _tokenLength);
for (int i = _tokenOffset; i <= _tokenLength - 1; i++)
{
var copyByte = copySequence[i % _tokenOffset];
copySequence[i] = copyByte;
}
// Move the position of the underlying stream back to the original position and write the
// CopySequence.
writer.BaseStream.Position = streamPosition;
writer.Write(copySequence);
}
internal static void UnPack(UInt16 packedToken, long position, out UInt16 unpackedOffset, out UInt16 unpackedLength)
{
// CALL CopyToken Help (section 2.4.1.3.19.1) returning LengthMask, OffsetMask, and BitCount.
var result = CopyToken.CopyTokenHelp(position);
// SET Length TO (Token BITWISE AND LengthMask) PLUS 3.
unpackedLength = (UInt16)((packedToken & result.LengthMask) + 3);
// SET temp1 TO Token BITWISE AND OffsetMask.
var temp1 = (UInt16)(packedToken & result.OffsetMask);
// SET temp2 TO 16 MINUS BitCount.
var temp2 = (UInt16)(16 - result.BitCount);
// SET Offset TO (temp1 RIGHT SHIFT BY temp2) PLUS 1.
unpackedOffset = (UInt16)((temp1 >> temp2) + 1);
}
/// <summary>
/// CopyToken Help derived bit masks are used by the Unpack CopyToken (section 2.4.1.3.19.2)
/// and the Pack CopyToken (section 2.4.1.3.19.3) algorithms. CopyToken Help also derives the
/// maximum length for a CopySequence (section 2.4.1.3.19) which is used by the Matching
/// algorithm (section 2.4.1.3.19.4).
/// The pseudocode uses the state variables described in State Variables (section 2.4.1.2):
/// DecompressedCurrent and DecompressedChunkStart.
/// </summary>
internal static CopyTokenHelpResult CopyTokenHelp(long difference)
{
var result = new CopyTokenHelpResult();
// SET BitCount TO the smallest integer that is GREATER THAN OR EQUAL TO LOGARITHM base 2
// of difference
result.BitCount = 0;
while ((1 << result.BitCount) < difference)
{
result.BitCount += 1;
}
// The number of bits used to encode Length MUST be greater than or equal to four. The
// number of bits used to encode Length MUST be less than or equal to 12
// SET BitCount TO the maximum of BitCount and 4
if (result.BitCount < 4)
result.BitCount = 4;
if (result.BitCount > 12)
throw new Exception();
// SET LengthMask TO 0xFFFF RIGHT SHIFT BY BitCount
result.LengthMask = (UInt16)(0xffff >> result.BitCount);
// SET OffsetMask TO BITWISE NOT LengthMask
result.OffsetMask = (UInt16)(~result.LengthMask);
// SET MaximumLength TO (0xFFFF RIGHT SHIFT BY BitCount) PLUS 3
result.MaximumLength = (UInt16)((0xffff >> result.BitCount) + 3);
return result;
}
public byte[] SerializeData()
{
var packedData = Pack(Position, _tokenOffset, _tokenLength);
return BitConverter.GetBytes(packedData);
}
#region Nested Classes
internal struct CopyTokenHelpResult
{
internal UInt16 LengthMask { get; set; }
internal UInt16 OffsetMask { get; set; }
internal UInt16 BitCount { get; set; } // offset bit count.
internal UInt16 MaximumLength { get; set; }
internal UInt16 LengthBitCount => (UInt16)(16 - BitCount);
}
#endregion
#region IEquatable
public static bool operator !=(CopyToken first, CopyToken second)
{
return !(first == second);
}
public static bool operator ==(CopyToken first, CopyToken second)
{
return Equals(first, second);
}
public override bool Equals(object obj)
{
return Equals(obj as CopyToken);
}
public bool Equals(IToken other)
{
return Equals(other as CopyToken);
}
public bool Equals(CopyToken other)
{
if (ReferenceEquals(other, null))
{
return false;
}
return other.Position == Position
&& other.Length == Length
&& other.Offset == Offset;
}
public override int GetHashCode()
{
return Position.GetHashCode() ^ Length.GetHashCode() ^ Offset.GetHashCode();
}
#endregion
}
/// <summary>
/// The DecompressedBuffer is a resizable array of bytes that contains the same data as the
/// CompressedContainer (section 2.4.1.1.1), but the data is in an uncompressed format.
/// </summary>
/// <remarks></remarks>
internal class DecompressedBuffer
{
internal DecompressedBuffer(byte[] uncompressedData)
{
using (var reader = new BinaryReader(new MemoryStream(uncompressedData)))
{
while (reader.BaseStream.Position < reader.BaseStream.Length)
{
var chunk = new DecompressedChunk(reader);
DecompressedChunks.Add(chunk);
}
}
}
internal DecompressedBuffer(CompressedContainer container)
{
foreach (var chunk in container.CompressedChunks)
{
DecompressedChunks.Add(new DecompressedChunk(chunk));
}
}
internal List<DecompressedChunk> DecompressedChunks { get; } = new List<DecompressedChunk>();
internal byte[] Data
{
get
{
using (var writer = new BinaryWriter(new MemoryStream()))
{
foreach (var chunk in DecompressedChunks)
{
writer.Write(chunk.Data);
}
using (var reader = new BinaryReader(writer.BaseStream))
{
reader.BaseStream.Position = 0;
return reader.ReadBytes((int) reader.BaseStream.Length);
}
}
}
}
}
/// <summary>
/// A DecompressedChunk is a resizable array of bytes in the DecompressedBuffer
/// (section 2.4.1.1.2). The byte array is the data from a CompressedChunk (section 2.4.1.1.4) in
/// uncompressed format.
/// </summary>
/// <remarks></remarks>
internal class DecompressedChunk
{
internal DecompressedChunk(CompressedChunk compressedChunk)
{
if (compressedChunk.Header.IsCompressed)
{
// Loop through all the data, get TokenSequences and decompress them.
using (var writer = new BinaryWriter(new MemoryStream()))
{
var tokens = ((CompressedChunkData)compressedChunk.ChunkData).TokenSequences;
foreach (var sequence in tokens)
{
sequence.Tokens.DecompressTokenSequence(writer);
}
var stream = (MemoryStream)writer.BaseStream;
var decompressedData = stream.GetBuffer();
Array.Resize(ref decompressedData, (int)stream.Length);
Data = decompressedData;
}
}
else
{
Data = compressedChunk.ChunkData.SerializeData();
}
}
internal DecompressedChunk(BinaryReader reader)
{
var bytesToRead = reader.BaseStream.Length - reader.BaseStream.Position;
if (bytesToRead > Globals.MaxBytesPerChunk)
bytesToRead = Globals.MaxBytesPerChunk;
Data = reader.ReadBytes((int) bytesToRead);
}
internal byte[] Data { get; }
}
internal static class Extensions
{
[DebuggerStepThrough]
internal static byte[] ToMcbsBytes(this string textToConvert, UInt16 codePage)
{
return Encoding.GetEncoding(codePage).GetBytes(textToConvert);
}
// http://stackoverflow.com/questions/321370/convert-hex-string-to-byte-array
internal static byte[] StringToByteArray(string hex)
{
return Enumerable.Range(0, hex.Length)
.Where(x => x % 2 == 0)
.Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
.ToArray();
}
}
internal static class Globals
{
internal const int MaxBytesPerChunk = 4096;
internal const int NumberOfChunkHeaderBytes = 2;
internal const byte PaddingByte = 0x0;
}
internal interface IChunkData
{
byte[] SerializeData();
int Size { get; }
}
internal interface IToken : IEquatable<IToken>
{
void DecompressToken(BinaryWriter writer);
byte[] SerializeData();
long Length { get; }
}
/// <summary>
/// A LiteralToken is a copy of one byte, in uncompressed format, from the DecompressedBuffer
/// (section 2.4.1.1.2).
/// </summary>
/// <remarks></remarks>
internal class LiteralToken : IToken, IEquatable<LiteralToken>
{
private readonly byte[] _data;
internal LiteralToken(BinaryReader dataReader)
{
_data = dataReader.ReadBytes(1);
}
internal LiteralToken(byte data)
{
_data = new [] { data };
}
public void DecompressToken(BinaryWriter writer)
{
writer.Write(_data);
writer.Flush();
}
public byte[] SerializeData()
{
return _data;
}
public long Length => 1L;
#region IEquatable
public static bool operator !=(LiteralToken first, LiteralToken second)
{
return !(first == second);
}
public static bool operator ==(LiteralToken first, LiteralToken second)
{
return Equals(first, second);
}
public override bool Equals(object obj)
{
return Equals(obj as LiteralToken);
}
public bool Equals(IToken other)
{
return Equals(other as LiteralToken);
}
public bool Equals(LiteralToken other)
{
if (ReferenceEquals(other, null))
{
return false;
}
return other._data.SequenceEqual(_data);
}
public override int GetHashCode()
{
return _data.GetHashCode();
}
#endregion
}
internal class RawChunk : IChunkData
{
private readonly byte[] _data;
public RawChunk(byte[] data)
{
_data = data;
}
public byte[] SerializeData()
{
return _data;
}
public int Size => _data.Length;
}
internal static class Tokenizer
{
internal static IEnumerable<TokenSequence> ToTokenSequences(this IEnumerable<IToken> tokens)
{
var accumulatedTokens = new List<IToken>();
foreach (var t in tokens)
{
if (accumulatedTokens.Count == 8)
{
yield return new TokenSequence(accumulatedTokens);
accumulatedTokens.Clear();
}
accumulatedTokens.Add(t);
}
if (accumulatedTokens.Count != 0)
{
yield return new TokenSequence(accumulatedTokens);
}
}
internal static void DecompressTokenSequence(this IEnumerable<IToken> tokens, BinaryWriter writer)
{
foreach (var token in tokens)
{
token.DecompressToken(writer);
}
}
internal static bool OverlapsWith(this CopyToken thisToken, CopyToken otherToken)
{
var firstToken = thisToken;
var secondToken = otherToken;
if (thisToken.Position > otherToken.Position)
{
firstToken = otherToken;
secondToken = thisToken;
}
// Contract.Assert(firstToken.Position <= secondToken.Position);
return firstToken.Position + firstToken.Length > secondToken.Position;
}
internal static bool Contains(this CopyToken thisToken, CopyToken otherToken)
{
var otherTokenStartsAfterThisToken = thisToken.Position <= otherToken.Position;
var otherTokenEndsBeforeThisToken = thisToken.Position + thisToken.Length >=
otherToken.Position + otherToken.Length;
return otherTokenStartsAfterThisToken && otherTokenEndsBeforeThisToken;
}
internal static IEnumerable<IToken> TokenizeUncompressedData(byte[] uncompressedData)
{
// The commented code is alternative to the specification for the compression.
//var possibleCopyTokens = AllPossibleCopyTokens(uncompressedData);
//var normalCopyTokens = NormalizeCopyTokens(possibleCopyTokens);
//var allTokens = WeaveTokens(normalCopyTokens, uncompressedData);
var copyTokens = GetSpecificationCopyTokens(uncompressedData);
var allTokens = WeaveTokens(copyTokens, uncompressedData);
foreach (var t in allTokens)
{
yield return t;
}
}
private static IEnumerable<CopyToken> GetSpecificationCopyTokens(byte[] uncompressedData)
{
var position = 0L;
while (position < uncompressedData.Length)
{
UInt16 offset = 0;
UInt16 length = 0;
Match(uncompressedData, position, out offset, out length);
if (length > 0)
{
yield return new CopyToken(position, offset, length);
position += length;
}
else
{
position++;
}
}
}
private static IEnumerable<CopyToken> AllPossibleCopyTokens(byte[] uncompressedData)
{
var position = 0L;
while (position < uncompressedData.Length)
{
UInt16 offset = 0;
UInt16 length = 0;
Match(uncompressedData, position, out offset, out length);
if (length > 0)
{
yield return new CopyToken(position, offset, length);
}
position++;
}
}
private static IEnumerable<CopyToken> NormalizeCopyTokens(IEnumerable<CopyToken> copyTokens)
{
var remainingTokens = RemoveRedundantTokens(copyTokens).ToList();
remainingTokens = RemoveOverlappingTokens(remainingTokens).ToList();
return remainingTokens;
}
private static IEnumerable<CopyToken> RemoveRedundantTokens(IEnumerable<CopyToken> tokens)
{
CopyToken previous = null;
foreach (var next in tokens)
{
if (previous == null)
{
previous = next;
continue;
}
if (previous.OverlapsWith(next))
{
//figure out which one to keep. There can only be one!
if (previous.Length >= next.Length)
{
yield return previous;
// can't return next.
}
else
{
yield return next;
}
}
else
{
yield return previous;
previous = next;
}
}
}
private static IEnumerable<CopyToken> RemoveOverlappingTokens(IEnumerable<CopyToken> tokens)
{
// create a list of the current tokens.
Node list = null;
foreach (var t in tokens.Reverse())
{
list = new Node(t, list);
}
// Contract.Assert(list != null);
return FindBestPath(list);
}
private static Node FindBestPath(Node node)
{
// Contract.Requires<ArgumentNullException>(node != null);
// find any overlapping tokens
Node bestPath = null;
foreach (var overlappingNode in GetOverlappingNodes(node))
{
var currentPath = new Node(overlappingNode.Value, null);
// find the next non-overlapping node.
var nonOverlappingNode = GetNextNonOverlappingNode(overlappingNode);
if (nonOverlappingNode != null)
{
currentPath.NextNode = FindBestPath(nonOverlappingNode);
}
if (bestPath == null
|| bestPath.Length < currentPath.Length)
{
bestPath = currentPath;
}
}
return bestPath;
}
private static IEnumerable<Node> GetOverlappingNodes(Node node)
{
// Contract.Requires<ArgumentNullException>(node != null);
var firstNode = node;
while (node != null
&& firstNode.Value.OverlapsWith(node.Value))
{
yield return node;
node = node.NextNode;
}
}
private static Node GetNextNonOverlappingNode(Node node)
{
// Contract.Requires<ArgumentNullException>(node != null);
var firstNode = node;
while (node != null
&& firstNode.Value.OverlapsWith(node.Value))
{
node = node.NextNode;
}
return node;
}
private static IEnumerable<IToken> WeaveTokens(IEnumerable<CopyToken> copyTokens, byte[] uncompressedData)
{
var position = 0L;
foreach (var currentCopyToken in copyTokens)
{
while (position < currentCopyToken.Position)
{
yield return new LiteralToken(uncompressedData[position]);
position++;
}
yield return currentCopyToken;
position += currentCopyToken.Length;
}
while (position < uncompressedData.Length)
{
yield return new LiteralToken(uncompressedData[position]);
position++;
}
}
internal static void Match(byte[] uncompressedData, long position, out UInt16 matchedOffset, out UInt16 matchedLength)
{
var decompressedCurrent = position;
var decompressedEnd = uncompressedData.Length;
const long decompressedChunkStart = 0;
// SET Candidate TO DecompressedCurrent MINUS 1
var candidate = decompressedCurrent - 1L;
// SET BestLength TO 0
var bestLength = 0L;
var bestCandidate = 0L;
// WHILE Candidate is GREATER THAN OR EQUAL TO DecompressedChunkStart
while (candidate >= decompressedChunkStart)
{
// SET C TO Candidate
var c = candidate;
// SET D TO DecompressedCurrent
var d = decompressedCurrent;
// SET Len TO 0
var len = 0;
// WHILE (D is LESS THAN DecompressedEnd)
// and (the byte at D EQUALS the byte at C)
while (d < decompressedEnd
&& uncompressedData[d] == uncompressedData[c])
{
// INCREMENT Len
len++;
// INCREMENT C
c++;
// INCREMENT D
d++;
} // END WHILE
// IF Len is GREATER THAN BestLength THEN
if (len > bestLength)
{
// SET BestLength TO Len
bestLength = len;
// SET BestCandidate TO Candidate
bestCandidate = candidate;
} // ENDIF
// DECREMENT Candidate
candidate--;
} // END WHILE
// IF BestLength is GREATER THAN OR EQUAL TO 3 THEN
if (bestLength >= 3)
{
// CALL CopyToken Help (section 2.4.1.3.19.1) returning MaximumLength
var result = CopyToken.CopyTokenHelp(decompressedCurrent);
// SET Length TO the MINIMUM of BestLength and MaximumLength
matchedLength = (UInt16)bestLength;
if (bestLength > result.MaximumLength)