/// <summary>
/// Decompress data.
/// </summary>
/// <param name="data">Data to be decompressed.</param>
/// <returns>Decompressed Data.</returns>
public byte[] Decompress(byte[] data)
{
int CurrentPosition = 0;
var result = new List <byte>();
/*
* Loop until a decompression terminating condition
* Build the decoding table
* CurrentPosition = 256 // start at the end of the Huffman table
* NextBits = Read16Bits(InputBuffer + CurrentPosition)
* CurrentPosition += 2
* NextBits <<= 16
* NextBits |= Read16Bits(InputBuffer + CurrentPosition)
* CurrentPosition += 2
* ExtraBits = 16
* BlockEnd = OutputPosition + 65536
*
* Loop until a block terminating condition
* If OutputPosition >= BlockEnd then terminate block processing
* Loop until a literal processing terminating condition
* Next15Bits = NextBits >> (32 – 15)
* HuffmanSymbol = DecodingTable[Next15Bits]
* HuffmanSymbolBitLength = the bit length of HuffmanSymbol, from the table in the input buffer
* If HuffmanSymbol <= 0
* NextBits <<= HuffmanSymbolBitLength
* ExtraBits -= HuffmanSymbolBitLength
*
* Do
* HuffmanSymbol = - HuffmanSymbol
* HuffmanSymbol += (NextBits >> 31)
* NextBits *= 2
* ExtraBits = ExtraBits - 1
* HuffmanSymbol = DecodingTable[HuffmanSymbol]
* While HuffmanSymbol <= 0
* Else
* DecodedBitCount = HuffmanSymbol & 15
* NextBits <<= DecodedBitCount
* ExtraBits -= DedcodedBitCount
*
* HuffmanSymbol >>= 4 // Shift by 4 bits to get the symbol value
* // (the lower 4 bits are the bit length of the symbol)
* HuffmanSymbol -= 256
* If ExtraBits < 0
* NextBits |= Read16Bits(InputBuffer + CurrentPosition) << (-ExtraBits)
* ExtraBits += 16
* CurrentPosition += 2
* If HuffmanSymbol >= 0
* If HuffmanSymbol == 0
* If the entire input buffer has been read and
* the expected decompressed size has been written to the output buffer
* Decompression is complete. Return with success.
* Terminate literal processing
* Else
* Output the byte value of HuffmanSymbol to the output stream
* End of literal processing Loop
*
* MatchLength = HuffmanSymbol mod 16
* MatchOffsetBitLength = HuffmanSymbol / 16
* If MatchLength == 15
* MatchLength = ReadByte(InputBuffer + CurrentPosition)
* CurrentPosition += 1
* If MatchLength == 255
* MatchLength = Read16Bits(InputBuffer + CurrentPosition)
* CurrentPosition += 2
* If MatchLength < 15
* The compressed data is invalid. Return error.
* MatchLength = MatchLength - 15
* MatchLength = MatchLength + 15
* MatchLength = MatchLength + 3
* MatchOffset = NextBits >> (32 – MatchOffsetBitLength)
* MatchOffset += (1 << MatchOffsetBitLength)
* NextBits <<= MatchOffsetBitLength
* ExtraBits -= MatchOffsetBitLength
* If ExtraBits < 0
* NextBits |= Read16Bits(InputBuffer + CurrentPosition) << (-ExtraBits)
* ExtraBits += 16
* CurrentPosition += 2
* For i = 0 to MatchLength - 1
* Output OutputBuffer[CurrentOutputPosition – MatchOffset + i]
* End of block loop
* End of decoding loop
*/
HuffmanHeader header = null;
uint NextBits = 0;
int BlockEnd = 0;
while (CurrentPosition < data.Length)
{
int remainingLength = data.Length - CurrentPosition;
if (remainingLength < 256)
{
/*
* Processing for the unhandled EOF in the last block if:
* 1. The decompressed size of last block is 65536.
* 2. Only two bytes are remained.
* 3. The unhandled symbol is EOF.
* 4. All remaining bits are zero.
*/
if (result.Count == BlockEnd && remainingLength == 2 && header != null)
{
uint Next15Bits = NextBits >> (32 - 15);
int HuffmanSymbol = header.DecodingTable[Next15Bits];
int HuffmanSymbolBitLength = header.len[HuffmanSymbol];
NextBits <<= HuffmanSymbolBitLength;
uint remainingBytes = Read16Bits(data, CurrentPosition);
CurrentPosition += 2;
if (HuffmanSymbol == 256 && NextBits == 0 && remainingBytes == 0)
{
continue;
}
}
throw new XcaException("[Data error]: Data in buffer is less than expected!");
}
header = new HuffmanHeader(data, CurrentPosition);
header.buildDecodingTable();
CurrentPosition += 256;
NextBits = Read16Bits(data, CurrentPosition);
CurrentPosition += 2;
NextBits <<= 16;
NextBits |= Read16Bits(data, CurrentPosition);
CurrentPosition += 2;
int ExtraBits = 16;
BlockEnd = result.Count + 65536;
while (result.Count < BlockEnd)
{
uint Next15Bits = NextBits >> (32 - 15);
int HuffmanSymbol = header.DecodingTable[Next15Bits];
int HuffmanSymbolBitLength = header.len[HuffmanSymbol];
NextBits <<= HuffmanSymbolBitLength;
ExtraBits -= HuffmanSymbolBitLength;
if (ExtraBits < 0)
{
NextBits |= Read16Bits(data, CurrentPosition) << (-ExtraBits);
ExtraBits += 16;
CurrentPosition += 2;
}
if (HuffmanSymbol < 256)
{
result.Add((byte)HuffmanSymbol);
}
else if (HuffmanSymbol == 256 && CurrentPosition == data.Length)
{
break;
}
else
{
HuffmanSymbol -= 256;
uint MatchLength = (uint)(HuffmanSymbol % 16);
int MatchOffsetBitLength = HuffmanSymbol / 16;
if (MatchLength == 15)
{
MatchLength = ReadByte(data, CurrentPosition);
CurrentPosition += 1;
if (MatchLength == 255)
{
MatchLength = Read16Bits(data, CurrentPosition);
CurrentPosition += 2;
if (MatchLength < 15)
{
throw new XcaException("[Data error]: MatchLength should not be less than 15!");
}
MatchLength -= 15;
}
MatchLength += 15;
}
MatchLength += 3;
int MatchOffset = (int)((ulong)NextBits >> (32 - MatchOffsetBitLength));
MatchOffset += (1 << MatchOffsetBitLength);
NextBits <<= MatchOffsetBitLength;
ExtraBits -= MatchOffsetBitLength;
if (ExtraBits < 0)
{
NextBits |= Read16Bits(data, CurrentPosition) << (-ExtraBits);
ExtraBits += 16;
CurrentPosition += 2;
}
var location = result.Count;
for (int i = 0; i < MatchLength; i++)
{
int matchPosition = location - MatchOffset + i;
if (matchPosition < 0 || matchPosition >= result.Count)
{
throw new XcaException("[Data error]: Match offset out of buffer!");
}
byte matchLiteral = result[matchPosition];
result.Add(matchLiteral);
}
}
}
}
return(result.ToArray());
}
/// <summary>
/// Decompress data.
/// </summary>
/// <param name="data">Data to be decompressed.</param>
/// <returns>Decompressed Data.</returns>
public byte[] Decompress(byte[] data)
{
var header = new HuffmanHeader(data.Take(256).ToArray());
var result = new List <byte>();
/*
* Build the decoding table
* CurrentPosition = 256 // start at the end of the Huffman table
* NextBits = Read16Bits(InputBuffer + CurrentPosition)
* CurrentPosition += 2
* NextBits <<= 16
* NextBits |= Read16Bits(InputBuffer + CurrentPosition)
* CurrentPosition += 2
* ExtraBits = 16
* Loop until a terminating condition
* Next15Bits = NextBits >> (32 – 15)
* HuffmanSymbol = DecodingTable[Next15Bits]
* HuffmanSymbolBitLength = the bit length of HuffmanSymbol, from the table in
* the input buffer
* NextBits <<= HuffmanSymbolBitLength
* ExtraBits -= HuffmanSymbolBitLength
* If ExtraBits < 0
* NextBits |= Read16Bits(InputBuffer + CurrentPosition) << (-ExtraBits)
* ExtraBits += 16
* CurrentPosition += 2
* If HuffmanSymbol < 256
* Output the byte value HuffmanSymbol to the output stream.
* Else If HuffmanSymbol == 256 and
* the entire input buffer has been read and
* the expected decompressed size has been written to the output buffer
* Decompression is complete. Return with success.
* Else
* HuffmanSymbol = HuffmanSymbol - 256
* MatchLength = HuffmanSymbol mod 16
* MatchOffsetBitLength = HuffmanSymbol / 16
* If MatchLength == 15
* MatchLength = ReadByte(InputBuffer + CurrentPosition)
* CurrentPosition += 1
* If MatchLength == 255
* MatchLength = Read16Bits(InputBuffer + CurrentPosition)
* CurrentPosition += 2
* If MatchLength < 15
* The compressed data is invalid. Return error.
* MatchLength = MatchLength - 15
* MatchLength = MatchLength + 15
* MatchLength = MatchLength + 3
* MatchOffset = NextBits >> (32 – MatchOffsetBitLength)
* MatchOffset += (1 << MatchOffsetBitLength)
* NextBits <<= MatchOffsetBitLength
* ExtraBits -= MatchOffsetBitLength
* If ExtraBits < 0
* Read the next 2 bytes the same as the preceding (ExtraBits < 0) case
* For i = 0 to MatchLength - 1
* Output OutputBuffer[CurrentOutputPosition – MatchOffset + i]
*/
header.buildDecodingTable();
int CurrentPosition = 256;
uint NextBits = Read16Bits(data, CurrentPosition);
CurrentPosition += 2;
NextBits <<= 16;
NextBits |= Read16Bits(data, CurrentPosition);
CurrentPosition += 2;
int ExtraBits = 16;
while (true)
{
uint Next15Bits = NextBits >> (32 - 15);
int HuffmanSymbol = header.DecodingTable[Next15Bits];
int HuffmanSymbolBitLength = header.len[HuffmanSymbol];
NextBits <<= HuffmanSymbolBitLength;
ExtraBits -= HuffmanSymbolBitLength;
if (ExtraBits < 0)
{
NextBits |= Read16Bits(data, CurrentPosition) << (-ExtraBits);
ExtraBits += 16;
CurrentPosition += 2;
}
if (HuffmanSymbol < 256)
{
result.Add((byte)HuffmanSymbol);
}
else if (HuffmanSymbol == 256 && CurrentPosition == data.Length)
{
break;
}
else
{
HuffmanSymbol -= 256;
uint MatchLength = (uint)(HuffmanSymbol % 16);
int MatchOffsetBitLength = HuffmanSymbol / 16;
if (MatchLength == 15)
{
MatchLength = ReadByte(data, CurrentPosition);
CurrentPosition += 1;
if (MatchLength == 255)
{
MatchLength = Read16Bits(data, CurrentPosition);
CurrentPosition += 2;
if (MatchLength < 15)
{
throw new XcaException("[Data error]: MatchLength should not be less than 15!");
}
MatchLength -= 15;
}
MatchLength += 15;
}
MatchLength += 3;
int MatchOffset = (int)((ulong)NextBits >> (32 - MatchOffsetBitLength));
MatchOffset += (1 << MatchOffsetBitLength);
NextBits <<= MatchOffsetBitLength;
ExtraBits -= MatchOffsetBitLength;
if (ExtraBits < 0)
{
NextBits |= Read16Bits(data, CurrentPosition) << (-ExtraBits);
ExtraBits += 16;
CurrentPosition += 2;
}
var location = result.Count;
for (int i = 0; i < MatchLength; i++)
{
int matchPosition = location - MatchOffset + i;
if (matchPosition < 0 || matchPosition >= result.Count)
{
throw new XcaException("[Data error]: Match offset out of buffer!");
}
byte matchLiteral = result[matchPosition];
result.Add(matchLiteral);
}
}
}
return(result.ToArray());
}