05 字典编码

int EncodeLZSSByFile(FILE *fpIn, FILE *fpOut)
{
    bit_file_t *bfpOut;

    encoded_string_t matchData;
    unsigned int i, c;
    unsigned int len;                       /* length of string */

    /* head of sliding window and lookahead */
    unsigned int windowHead = 0, uncodedHead = 0;

    /* convert output file to bitfile */
    bfpOut = MakeBitFile(fpOut, BF_WRITE);
    
    /************************************************************************
    * Fill the sliding window buffer with some known vales.  must
    * use the same values.  If common characters are used, there's an
    * increased chance of matching to the earlier strings.
    ************************************************************************/
    memset(slidingWindow, ' ', WINDOW_SIZE * sizeof(unsigned char));

    /************************************************************************
    * Copy MAX_CODED bytes from the input file into the uncoded lookahead
    * buffer.
    ************************************************************************/
    for (len = 0; len < MAX_CODED && (c = getc(fpIn)) != EOF; len++)
    {
        uncodedLookahead[len] = c;
    }

    if (len == 0)
    {
        return EXIT_SUCCESS;   /* inFile was empty */
    }

    /* Look for matching string in sliding window */

    matchData = FindMatch(windowHead, uncodedHead);

    /* now encoded the rest of the file until an EOF is read */
	/* 未编码的剩余字符数*/
    while (len > 0)
    {
        if (matchData.length > len)
        {
            /* garbage beyond last data happened to extend match length */
            matchData.length = len;
        }

        if (matchData.length <= MAX_UNCODED)
        {
            /* not long enough match.  write uncoded flag and character */
            BitFilePutBit(UNCODED, bfpOut);
            BitFilePutChar(uncodedLookahead[uncodedHead], bfpOut);

            matchData.length = 1;   /* set to 1 for 1 byte uncoded */
        }
        else
        {
            unsigned int adjustedLen;

            /* adjust the length of the match so minimun encoded len is 0*/
            adjustedLen = matchData.length - (MAX_UNCODED + 1);

            /* match length > MAX_UNCODED.  Encode as offset and length. */
            BitFilePutBit(ENCODED, bfpOut);
            BitFilePutBitsInt(bfpOut, &matchData.offset, OFFSET_BITS,sizeof(unsigned int));
            BitFilePutBitsInt(bfpOut, &adjustedLen, LENGTH_BITS,sizeof(unsigned int));
        }

        /********************************************************************
        * Replace the matchData.length worth of bytes we've matched in the
        * sliding window with new bytes from the input file.
        ********************************************************************/
        i = 0;
        while ((i < matchData.length) && ((c = getc(fpIn)) != EOF))
        {
            /* add old byte into sliding window and new into lookahead */
            ReplaceChar(windowHead, uncodedLookahead[uncodedHead]);
            uncodedLookahead[uncodedHead] = c;
            windowHead = Wrap(windowHead + 1, WINDOW_SIZE);
            uncodedHead = Wrap(uncodedHead + 1, MAX_CODED);
            i++;
        }

        /* handle case where we hit EOF before filling lookahead */
        while (i < matchData.length)
        {
            ReplaceChar(windowHead, uncodedLookahead[uncodedHead]);
            /* nothing to add to lookahead here */
            windowHead = Wrap(windowHead + 1, WINDOW_SIZE);
            uncodedHead = Wrap(uncodedHead + 1, MAX_CODED);
            len--;
            i++;
        }

        /* find match for the remaining characters */
        matchData = FindMatch(windowHead, uncodedHead);
    }

    /* we've decoded everything, free bitfile structure */
    BitFileToFILE(bfpOut);

   return (EXIT_SUCCESS);
}