Huffman Compression
A minimal huffman compression program using C++ language.
Theory
Huffman compression is based on huffman coding technique. The huffman coding creates an optimal binary tree that is constructed based on frequency of an item/character in a file.
Let's take an example of a file or string containing data like "AAABBCAAADDFFAAAADCCCDAADDDAAACGAAACACA"
character frequency
A 20
B 2
C 7
D 7
F 2
G 1
The above following data will generate a binary tree starting from the characters having the lowest frequency, and construct till we use all the characters as follows:
Pass 1:
(A, 20) (C, 7) (D, 7) (B, 2) (F, 2) (G, 1) (A, 20) (C, 7) (D, 7) (**, 3) (B, 2)
=> / \
/ \
(F, 2) (G, 1)
Pass 2:
(A, 20) (C, 7) (D, 7) (**, 3) (B, 2) (A, 20) (C, 7) (D, 7) (**, 5)
/ \ / \
/ \ / \
(F, 2) (G, 1) => (**, 3) (B, 2)
/ \
/ \
(F, 2) (G, 1)
Pass 3:
(A, 20) (C, 7) (D, 7) (**, 5) (A, 20) (C, 7) (**, 12)
/ \ / \
/ \ / \
(**, 3) (B, 2) => (D, 7) (**, 5)
/ \ / \
/ \ / \
(F, 2) (G, 1) (**, 3) (B, 2)
/ \
/ \
(F, 2) (G, 1)
Pass 4:
(A, 20) (**, 12) (C, 7) (A, 20) (**, 19)
/ \ / \
/ \ / \
(D, 7) (**, 5) (**, 12) (C, 7)
/ \ / \
/ \ => / \
(**, 3) (B, 2) (D, 7) (**, 5)
/ \ / \
/ \ / \
(F, 2) (G, 1) (**, 3) (B, 2)
/ \
/ \
(F, 2) (G, 1)
Pass 5 (Final), with huffman code:
Left Branch denoting 0 and right 1
(A, 20) (**, 19) (**, 39)
/ \ / \
/ \ (0)/ \(1)
(**, 12) (C, 7) [0] <= (A, 20) (**, 19)
/ \ / \
/ \ (0)/ \(1)
(D, 7) (**, 5) => (**, 12) (C, 7) => [11]
/ \ / \
/ \ (0)/ \(1)
(**, 3) (B, 2) [100] <= (D, 7) (**, 5)
/ \ / \
/ \ / \(1)
(F, 2) (G, 1) (**, 3) (B, 2) => [1011]
/ \
(0)/ \(1)
[10100] <= (F, 2) (G, 1) => [10101]
Final Huffman Codes:
character frequency Huffman Codes Actual Binary
A 20 0 01000001
B 2 1011 01000010
C 7 11 01000011
D 7 100 01000100
F 2 10100 01000110
G 1 10101 01000111
__________________________________________________________________
39 75 312
Hence the resultant data is stored as binary written as '000101110110001001001010010100000010011111110000100100100000111010100011011000000', which has 75 bits plus 5 digits appended to round off the remaining bits while storing in the file.
Executing program
g++ huffman-compression.cpp
[a.exe | ./a.out] -c|-dc [filename_to_be_compressed]
(The order must be same: first: option to compress/decompress and then second: filename)
The file to be compressed will generate a file with extension '.abiz', which is the compressed version of the original one.
Note:
- Compressing files other than ASCII based text files (e.g., audio (.mp3), video (.mp4), pdfs, document (.doc/.docx), etc.) can have little or no effect on the resulting size.