Huffman Algorithm for File Compression

https://github.com/TheNilesh/huffman/
License: Public Domain, no warranty
Nilesh Akhade

About

Huffman Algorithm is an efficient way for file Compression and Decompression. This program exactly follows huffman algorithm. It reads frequent characters from input file and replaces them with shorter binary codeword. The original file can be produced again without losing any bit.

Usage

Compression:

	./encode <file to compress>

Output file named .hzip will be produced. Decompression:

	./decode <file to uncompress>

File Structure

N= total number of unique characters(1 byte)
Character[1 byte]	Binary codeword String Form[MAX bytes]
Character[1 byte]	Binary codeword String Form[MAX bytes]
N times
p (1 byte)	p times 0's (p bits)
DATA

p = Padding done to ensure file fits in whole number of bytes. eg, file of 4 bytes + 3 bits must ne padded by 5 bits to make it 5 bytes.

Example

Text: aabcbaab

Content	Comment
3	N=3 (a,b,c)
a "1"	character and corresponding code "1"
b "01"	character and corresponding code "01"
c "00"	character and corresponding code "00"
4	Padding count
[0000]	Padding 4 zeroes
[1] [1] [01] [00] [01] [1] [1] [01]	Actual data, code in place of char

Algorithm

0. (Pass 1) Read input file
1. Create sorted linked list of characters from file, as per character frequency

   for eah character ch from file
   
    if( ch available in linked list at node p) then 
    {
    	p.freq++;
    	sort Linked list as per node's freq;
    }
    else
    	add new node at beginning of linked list with frequency=1;
   

2. Construct huffman tree from linked list 0. Create new node q, join two least freq nodes to its left and right 0. Insert created node q into ascending list 0. Repeat i & ii till only one node remains, i.e, ROOT of h-tree 0. Traverse tree in preorder mark each node with its codeword. simultaneously Recreate linked list of leaf nodes.
3. Write Mapping Table(character to codeword) to output file.
4. (Pass 2) Read input file.
5. Write codeword in place of each character in input file to output file for each character ch from input file write corresponding codeword into o/p file (lookup in mapping table OR linked list)
6. End

Contributing

Please feel free to submit issues and pull requests. I appreciate bug reports. Testing on different platforms is especially appreciated. I only tested on Linux.

License

This software is in the Public Domain. That means you can do whatever you like with it. That includes being used in proprietary products without attribution or restrictions. There are no warranties and there may be bugs.

Formally we are using CC0 - a Creative Commons license to place this work in the public domain. A copy of CC0 is in the LICENSE file.

"CC0 is a public domain dedication from Creative Commons. A work released
under CC0 is dedicated to the public domain to the fullest extent permitted
by law. If that is not possible for any reason, CC0 also provides a lax,
permissive license as a fallback. Both public domain works and the lax
license provided by CC0 are compatible with the GNU GPL."
  - http://www.gnu.org/licenses/license-list.html#CC0

Development

To do:

• Binary files, like jpeg,mp3 support
• Run scan to group repeating bit patterns, not bit.
• Unicode support