private string encode(string originalString)
{
	string compressedString = originalString.Substring(0, 1);
	string encodeChar = null;

	for (int n=161;n<191;n++) 
	{ //- Find a character not in the file to use in the encoding formatting
		string c = new string(((char)n), 1);
		
		if (originalString.IndexOf(c, 0, originalString.Length) == -1) 
		{
			encodeChar = c;
			break;
		}
	}

	if (encodeChar == null) 
	{
		MessageBox.Show("This file can't be compressed (No free character found)");
		return "";
	}

	int[] findBestResult = new int[2]; // store position and sequence length 

	int currPos = 1;
	int radix = 114; // the number base
	int bufferSize = radix*radix-1; // history buffer size
	int lookAheadBufferSize = radix-1; // max number of characters to copy in a sequence
	string lookAheadString = originalString.Substring(currPos, Math.Min(originalString.Length-currPos, lookAheadBufferSize));

	while (lookAheadString.Length > 0) // while there are characters to encode
	{
		encodeFindBest(originalString, Math.Max(currPos-bufferSize, 0), currPos-1, lookAheadString, findBestResult); // try to find an upcoming sequence in the history buffer and refer to it
		if (findBestResult[0] == -1) // no sequence found, just move 1 character forward and add the current character to the coded sequence
		{
			compressedString += originalString.Substring(currPos, 1);
			currPos++;
		} 
		else // a sequence was found, convert the position and sequence length to ASCII characters
		{
			int p = currPos-findBestResult[0];
			int l = findBestResult[1];
			int ms = (int)(p/radix);
			int ls = p-ms*radix;
			compressedString += encodeChar + new string((char)(14+ms), 1) + new string((char)(14+ls), 1) + new string((char)(14+l), 1);
			currPos += l;
		}

		lookAheadString = originalString.Substring(currPos, Math.Min(originalString.Length-currPos, lookAheadBufferSize));
	}

	return "v1.0 " + encodeChar +  compressedString;
}


private void encodeFindBest(string str, int winStart, int winEnd, string lookAhead, int[] res) 
{
	int lookAheadLength = lookAhead.Length;
	string winStr = str.Substring(winStart, winEnd-winStart);
	int sequenceLength = 5;
	int matchLength = 0;
	int matchPos = 0;
	int n;

	while (sequenceLength <= lookAheadLength) 
	{
		n = winStr.IndexOf(lookAhead.Substring(0, sequenceLength));
		if (n == -1) 
		{
			break;
		}
		else 
		{
			matchLength = sequenceLength;
			matchPos = n;
		}
		sequenceLength++;
	}

	if (matchLength > 0) 
	{
		res[0] = winStart+matchPos;
		res[1] = matchLength;
	}
	else 
	{
		res[0] = -1;
	}
}