/// <summary>
/// BitStringLookup function.
/// </summary>
/// <param name="bstr">
/// BITSTRING to look up.
/// </param>
/// <param name="n"></param>
/// <returns></returns>
public UInt32 BitStringLookup(ref BITSTRING bstr, UInt32 n)
{
if (n == 0)
{
return(0);
}
else
{
return(bstr.mask >> (int)(32 - n));
}
}
/// <summary>
/// Initializes BitString
/// </summary>
/// <param name="bstr">
/// BITSTRING to initialize.
/// </param>
/// <param name="source">
/// Source array
/// </param>
/// <param name="index">
/// Index value
/// </param>
public void BitStringInit(ref BITSTRING bstr, byte[] source, UInt32 index)
{
bstr.mask = BitConverter.ToUInt16(source, (int)index);
bstr.mask = bstr.mask << 16;
index = index + 2;
bstr.mask = bstr.mask + BitConverter.ToUInt16(source, (int)index);
index = index + 2;
bstr.bits = 32;
bstr.source = source;
bstr.index = index;
}
/// <summary>
/// BitStringSkip function
/// </summary>
/// <param name="bstr"></param>
/// <param name="n"></param>
public void BitStringSkip(ref BITSTRING bstr, UInt32 n)
{
bstr.mask = bstr.mask << (int)n;
bstr.bits = bstr.bits - (Int32)n;
if (bstr.bits < 16)
{
bstr.mask = bstr.mask + (UInt32)(BitConverter.ToUInt16(bstr.source, (int)bstr.index)
<< (int)(16 - bstr.bits));
bstr.index = bstr.index + 2;
bstr.bits = bstr.bits + 16;
}
}
/// <summary>
/// PrefixCodeTreeDecodeSymbol method decodes the symbols.
/// </summary>
/// <param name="bstr"></param>
/// <param name="root">
/// Used to traverse the tree.
/// </param>
/// <returns></returns>
public UInt32 PrefixCodeTreeDecodeSymbol(ref BITSTRING bstr, PrefixCodeNode root)
{
UInt32 bit;
PrefixCodeNode node = root;
do
{
bit = BitStringLookup(ref bstr, 1);
BitStringSkip(ref bstr, 1);
node = node.Child[bit];
} while (node.leaf == false);
return(node.symbol);
}
/// <summary>
/// This method is called to decompress the compressed data
/// </summary>
/// <param name="input">
/// Compressed Byte Array
/// </param>
/// <param name="outputSize">
/// Uncompressed Output Size
/// </param>
/// <param name="outputBuffer">
/// Decompressed output buffer.
/// </param>
public void Decompress(byte[] input, UInt32 outputSize, out byte[] outputBuffer)
{
byte[] output = new byte[outputSize];
UInt32 i = 0;
UInt32 stopIndex = i + outputSize;
UInt32 symbol;
UInt32 length;
Int32 offset;
PrefixCodeNode root = new PrefixCodeNode();
PrefixCodeNode[] prefixCodeTreeNodes = new PrefixCodeNode[1024];
for (int count = 0; count < 1024; count++)
{
prefixCodeTreeNodes[count] = new PrefixCodeNode();
}
BITSTRING bstr = new BITSTRING();
root = PrefixCodeTreeRebuild(input, ref prefixCodeTreeNodes);
BitStringInit(ref bstr, input, 256);
while (i < stopIndex)
{
symbol = PrefixCodeTreeDecodeSymbol(ref bstr, root);
if (symbol < 256)
{
output[i] = (byte)symbol;
i++;
}
else
{
symbol = symbol - 256;
length = symbol & 15;
symbol = symbol >> 4;
offset = (int)((1 << (int)symbol) + BitStringLookup(ref bstr, symbol));
offset = (-1) * offset;
if (length == 15)
{
length = bstr.source[bstr.index] + (UInt32)15;
bstr.index = bstr.index + 1;
if (length == 270)
{
length = BitConverter.ToUInt16(bstr.source, (int)bstr.index);
bstr.index = bstr.index + 2;
}
}
BitStringSkip(ref bstr, symbol);
length = length + 3;
do
{
output[i] = output[i + offset];
i++;
length--;
} while (length != 0);
}
}
outputBuffer = output;
}
