/*
*-------------------------------------------------------------------------------
* 4.1 LZSS_CompressData
*-------------------------------------------------------------------------------
*
* LZSS compress data
*
* This routine compress data from an in buffer using the LZSS algorithm. LZSS is
* a dictionary compression method where the dictionary is a sliding window. The
* routine uses a look-ahead buffer and finds matches in previously read bytes
* stored in a sliding window.
* If a match is found an index/length pair is written to the output buffer
* (index is the position in the sliding window). If no match is found the read
* byte is just bypassed to the out buffer. To indicate if the data is an
* index/length pair or a plain text byte a single bit is used as indicator flag
* and is written to the out buffer.
* To speed up the compression a binary tree is used for storing previously
* compressed data.
*
* param inBuf Input data buffer with byte access
* param outBuf output data buffer with bit access
*
* return void
*
*/
public static byte[] LZSS_CompressData(byte[] inBuf)
{
/** Index var. for loop */
int i = 0;
/** Byte read from input stream */
int inByte = 0;
/** Number of bytes in the look head buffer */
int aheadBytes = 0;
/** Current position in the window */
int winPos = 1;
/** Number of bytes to replace in the window */
int replCnt = 0;
/** Length of the data match found in the window */
int matchLen = 0;
/** Position in the window of the data match */
int matchPos = 0;
/** Indicator of End Of Stream reached */
bool eosReached = false;
BitQuery Result = new BitQuery();
BitQuery BQ = new BitQuery(inBuf);
/* Start with filling up the look-ahead buffer */
while ((aheadBytes < LZSS_LOOK_AHEAD_SIZE) && (!eosReached))
{
/* Get next input byte */
inByte = BQ.GetByte();
/* If input stream is finished, exit */
if (inByte == LZSS_END_OF_INPUT_STREAM)
{
eosReached = true;
}
else
{
/* Add byte to wondow */
LZSS_window[winPos + aheadBytes] = inByte;
/* Increase look-ahead bytes*/
aheadBytes = (aheadBytes + 1) & 0xFF;
}
}
/* Initialize the tree */
LZSS_InitTree(winPos);
/* While there still are bytes in the look ahead buffer, loop */
while (aheadBytes > 0)
{
/* If previously match length greater than look ahead bytes it's
* not possible to code correctly */
if (matchLen > aheadBytes)
{
/* Set matched length to look-ahead buffer length */
matchLen = aheadBytes;
}
/* If the match is smaller than the compressed data (position/length-
* pair) there will be negative compression so just output the byte */
if (matchLen <= LZSS_BREAK_EVEN)
{
/* Set consumed bytes in input stream to 1 */
replCnt = 1;
/* Indicate that next byte in output stream is uncompressed
* by output a '1' */
Result.PutBit(1);
/* Output uncompressed byte */
Result.PutBits(LZSS_window[winPos], 8);
}
/* The match is larger than a position/length pair, compression can be
* done */
else
{
/* Indicate that the following bits are compressed data by output a
* '0' */
Result.PutBit(0);
/* Output position in the window */
Result.PutBits(matchPos, LZSS_INDEX_BIT_COUNT);
/* Output the length of the match, (length is the number of bytes
* that is greater than LZSS_BREAK_EVEN) */
Result.PutBits((matchLen - (LZSS_BREAK_EVEN + 1)),
LZSS_LENGTH_BIT_COUNT);
/* Set consumed bytes in input stream to the length of the match */
replCnt = matchLen;
}
/* Delete consumed bytes and add new bytes in the window */
for (i = 0; i < replCnt; i++)
{
/* Remove consumed byte from the window */
LZSS_DeleteNode(LZSS_MOD_WINDOW(winPos +
(UInt16)LZSS_LOOK_AHEAD_SIZE));
/* Get next input byte */
inByte = BQ.GetByte();
/* If input stream is finished */
if (inByte == LZSS_END_OF_INPUT_STREAM)
{
/* Decrease the look-ahead bytes */
aheadBytes = (aheadBytes - 1) & 0xFF;
}
else
{
/* Add the new byte from the input stream to the window */
LZSS_window[LZSS_MOD_WINDOW(winPos + LZSS_LOOK_AHEAD_SIZE)] = inByte;
}
/* Increase the position in the window */
winPos = LZSS_MOD_WINDOW(winPos + 1);
/* If there still are bytes in the look-ahead buffer */
if (aheadBytes != 0)
{
/* Add byte position to the tree and get the length of the
* match */
matchLen = LZSS_AddNode(winPos, ref matchPos);
}
}
}
/* Input stream finished, write end of stream to the output buffer
* uncompressed */
//OutputBit(outBuf, (Uint8_T)0);
Result.PutBit(0);
//OutputBits(outBuf, (Uint32_T)LZSS_END_OF_STREAM, LZSS_INDEX_BIT_COUNT);
Result.PutBits(LZSS_END_OF_STREAM, LZSS_INDEX_BIT_COUNT);
return Result.Export();
}
