DESCRIPTION
-----------
This archive contains a simple and readable ANSI C implementation of
Lempel-Ziv-Welch coding and decoding.  This implementation is not intended to
be the best, fastest, smallest, or any other performance related adjective.

More information on lzw encoding may be found at:
https://michaeldipperstein.github.io/lzw.html

FILES
-----
COPYING         - Rules for copying and distributing GPL software
COPYING.LESSER  - Rules for copying and distributing LGPL software
lzw.h           - Header containing prototypes for lzw library functions.
lzwdecode.c     - Source for library lzw decoding routines.
lzwencode.c     - Source for library lzw encoding routines.
Makefile        - makefile for this project (assumes gcc compiler and GNU make)
README          - this file
sample.c        - Demonstration of how to use the lzw library functions
optlist/        - Subtree containing optlist command line option parser library
bitfile/        - Subtree containing bitfile bitwise file library

BUILDING
--------
To build these files with GNU make and gcc, simply enter "make" from the
command line.  The executable will be named sample (or sample.exe).

USAGE
-----
Usage: sample <options>

options:
  -c : Encode input file to output file.
  -d : Decode input file to output file.
  -i <filename> : Name of input file.
  -o <filename> : Name of output file.
  -h|?  : Print out command line options.

-c      Compress the specified input file (see -i) using the Lempel-Ziv-Welch
        encoding algorithm.  Results are written to the specified output file
        (see -o).

-d      Decompress the specified input file (see -i) using the Lempel-Ziv-Welch
        decoding algorithm.  Results are written to the specified output file
        (see -o).  Only files compressed by this program may be decompressed.

-i <filename>   The name of the input file.  There is no valid usage of this
                program without a specified input file.

-o <filename>   The name of the output file.  If no file is specified, stdout
                will be used.  NOTE: Sending compressed output to stdout may
                produce undesirable results.
LIBRARY API
-----------
Encoding Data:
int LZWEncodeFile(FILE *fpIn, FILE *fpOut);
fpIn
    The file stream to be encoded.  It must opened.  NULL pointers will return
    an error.
fpOut
    The file stream receiving the encoded results.  It must be opened.  NULL
    pointers will return an error.
Return Value
    Zero for success, -1 for failure.  Error type is contained in errno.  Files
    will remain open.

Decoding Data:
int LZWDecodeFile(FILE *fpIn, FILE *fpOut);
fpIn
    The file stream to be decoded.  It must be opened.  NULL pointers will
    return an error.
fpOut
    The file stream receiving the decoded results.  It must be opened.  NULL
    pointers will return an error.
Return Value
    Zero for success, -1 for failure.  Error type is contained in errno.  Files
    will remain open.

HISTORY
-------
02/20/05  - Initial Release
03/27/05  - Utilizes variable code word length
04/20/05  - Separated encoding and decoding routines
          - Uses binary tree for encoding dictionary structure
06/21/05  - Corrected BitFileGetBits/PutBits error that accessed an extra
            byte when given an integral number of bytes.
08/30/07  - Explicitly licensed under LGPL version 3.
          - Replaces getopt() with optlist library.
12/21/09  - Fixed bug that occurs when output code word grows by two or more
            bits.
            Used BitFilePutBitsInt/BitFileGetBitsInt to allow for code words
            as large as sizeof(int).  (#define limits code words to 20 bits).
04/12/15  - Changed return value to 0 for success and -1 for failure with
            reason in errno.
          - Removed unused macros and declarations.
          - Upgraded to latest oplist and bitfile libraries.
          - Tighter adherence to Michael Barr's "Top 10 Bug-Killing Coding
            Standard Rules" (http://www.barrgroup.com/webinars/10rules).
07/16/17  - Changes for cleaner use with GitHub

TODO
----
- Do something to handle the case where the string table is full and does not
  contain entries for strings that are being encoded.
  - possibly purge and regenerate table after coding drops below X% hits
  - possibly replace least recently used code word (LRU) with new code
  - possibly start second dictionary when first is X% full and switch at
    TBD event
- Speed up code word search during compression
  - try AVL or Red/Black trees
  - maybe something similar to a Fibonacci heap
- Use typedefs and more type size checking for better portability

AUTHOR
------
Michael Dipperstein (mdipperstein@gmail.com)
https://michaeldipperstein.github.io