Compression-Selective_Decompression

Elias-Fano compression implementation in Python, created for the Data Structures and Algorithms course. The script reads a list of integers from a file, compresses them into two bit arrays (L and U), and prints the compressed representation along with their SHA-256 hash.

The repository where the task was published is here.

Overview

This Python script implements the Elias-Fano compression technique for a sorted list of integers. The program reads a list of integers from a file, compresses it using two bit arrays (L and U), and prints the compressed representations along with their SHA-256 hash.

Features

• Input Handling: Reads integers from a specified input file.
• Compression: Compresses the integers using the Elias-Fano scheme into two bit arrays, L and U.
• Output: Prints the bit arrays L and U in binary format.
• Hashing: Generates and prints the SHA-256 hash of the concatenated bit arrays L and U.

Files

• elias_fano.py: Main script containing the compression implementation.
• README.md: Documentation for the project.
• example_*.txt : Example input files used for testing.

Requirements

• Python 3.x
• Required Libraries: sys, math, hashlib

Usage

To run the script, use the following command:

python elias_fano.py <input_file>

where <input_file> is the path to the file containing the list of integers.

Implementation Details

Steps:

1. Reading Input: The script reads integers from the input file and stores them in a list.
2. Calculating Parameters:
   • n: Number of integers.
   • m: Maximum integer in the list.
   • l: Number of bits used for the least significant part, calculated as int(math.log(m / n, 2)).
3. Creating Bit Arrays:
   • L: Contains the last l bits of each integer.
   • U: Encodes the remaining bits in unary form.
4. Populating Bit Arrays:
   • The script splits each integer into parts for L and U and fills the respective bit arrays.
5. Output: Prints the bit arrays L and U in binary format and the SHA-256 hash of the concatenated arrays.

Notes

• Ensure the input file contains integers, each on a new line.
• The script does not handle input errors or invalid data types.

Author

• Aris Fetzian

License

This project is licensed under the MIT License.