DESCRIPTION
-----------
This archive contains a simple and readable ANSI C library implementing LZSS
encoding and decoding.  This implementation is not intended to be the best,
fastest, smallest, or any other performance related adjective.

Included in this library is a sample program demonstrating the usage of the
encode and decoding routines.  The library has been designed so that it may
be linked with different sliding window search routines which can speed up
the compression time at the cost of additional memory space.

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


FILES
-----
COPYING         - Rules for copying and distributing LGPL software
brute.c         - File implementing brute force search for strings matching the
                  strings to be encoded.
COPYING         - Rules for copying and distributing GPL software
COPYING.LESSER  - Rules for copying and distributing LGPL software
hash.c          - File implementing hash table search for strings matching the
                  strings to be encoded.
kmp.c           - File implementing the Knuth-Morris-Pratt string matching
                  algorithm to search for strings matching the strings to be
                  encoded.
list.c          - File implementing linked list indexed search for strings
                  matching the strings to be encoded.
lzlocal.h       - Header file defining interface to be used by files
                  implementing searches for strings matching strings to be
                  encoded.
lzdecode.c      - LZSS decoding source
lzencode.c      - LZSS encoding source
lzss.h          - LZSS encoding/decoding header files
lzvars.c        - Variables used by both lzencode and lzdecode
Makefile        - makefile for this project (assumes gcc compiler and GNU make)
README          - this file
sample.c        - Sample program demonstrating usage of encode and decode
                  routines.
tree.c          - File implementing a sorted binary tree to index and search
                  for strings matching the strings to be encoded.
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:
1. Edit the Makefile variable FMOBJ to choose the string matching technique
   which will be used.
2. Windows users should define the environment variable OS to be Windows or
   Windows_NT.  This is often already done.
3. Enter the command "make" from the command line.


The sample programs comp and decomp are not built by default.  To build these
programs on Unix/Linux use the commands "make comp" and "make decomp".  Windows
users should use the commands "make comp.exe" and "make decomp.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      Performs LZSS style compression on specified input file (see -i)
        writing the results to the specified output file (see -o).

-d      Decompresses the specified input file (see -i) writing the results 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.  There is no valid usage of this
                program without a specified input file.

LIBRARY API
-----------
Encoding Data:
int EncodeLZSS(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 DecodeLZSS(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
-------
11/24/03  - Initial release
12/10/03  - Changed handling of sliding window to better match standard
            algorithm description.
12/11/03  - Added version with linked lists to speed up encode.
12/12/03  - Added version with hash table to speed up encode.
02/21/04  - Major changes:
            * Separated encode/decode, match finding, and main.
            * Use bitfiles for reading/writing files
            * Use traditional LZSS encoding where the coded/uncoded bits
              precede the symbol they are associated with, rather than
              aggregating the bits.
11/08/04  - Major changes:
            * Split encode and decode routines for to allow for separate
              linking (see comp.c and decomp.c)
            * Makefile now builds code as libraries.  This should make LGPL
              compliance a bit easier.
            * Upgraded to latest bitfile library.
            * Add the option to pass compression/decompression routines file
              pointers instead of file names.
06/21/05  - Corrected BitFileGetBits/PutBits error that accessed an extra
            byte when given an integral number of bytes.
12/27/05  - Major changes:
            * Use slower but clearer Get/PutBitsInt for reading/writing bits.
            * Replace mod with conditional Wrap macro.
            * Allow hash table to change size with dictionary.
12/25/06  - Corrected bug in allocation of default decode output.
          - Minor comment corrections
03/24/07  - Closes output file in EncodeLZSSByName and DecodeLZSSByName
08/30/07  - Explicitly licensed under LGPL version 3.
          - Replaces getopt() with optlist library.
02/11/10  - Added code that uses the Knuth-Morris-Pratt string matching
            algorithm to search for string matches during the encoding process.
08/16/10  - Added code that uses a binary tree to sort strings as they are
            added to the sliding window and to search for string matches during
            the encoding process.
11/30/14  - Corrected binary tree code for adding a new character into the
            sliding window dictionary.
          - Changed return value to 0 for success and -1 for failure with
            reason in errno.
          - 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 easier use with GitHub
11/02/20  - Pass sliding window and uncoded lookahead as a parameter instead
            of using global variables.
          - Short circuit match finding for short lookahead buffers.

TODO
----
- Experiment with string matching techniques and data structures
  - suffix trees
  - suffix arrays
  - multi-byte hash keys
  - Boyer-Moore
  - hash/binary tree combo, using one tree for each hash key
- Use a lazy encoding process.
  - Defer writing a code word until it is determined that a longer match
    isn't formed by adding the next symbols from the unecoded stream.

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