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); }