76 lines
2.1 KiB
Python
76 lines
2.1 KiB
Python
#!/usr/bin/env python
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# -*- coding: utf-8 -*-
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"""
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This module provides encoding and decoding functions for Hamming codes
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(C) 2022 Louis Heredero louis.heredero@edu.vs.ch
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"""
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class HammingError(Exception):
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pass
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def encode(data, blocksize=7):
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result = []
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datasize = blocksize-blocksize.bit_length()
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data = list(map(int, data))
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if len(data) % datasize:
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raise HammingError(f"Length of data is not a multiple of {datasize}")
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nblocks = int(len(data)/datasize)
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for b in range(nblocks):
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for i in range(blocksize):
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# Power of 2
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if (i+1)&i == 0 or i == 0:
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result.append(0)
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else:
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result.append(data.pop(0))
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for i in range(blocksize.bit_length()):
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p = 1 << i
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c = sum([result[b*blocksize+j] for j in range(blocksize) if (j+1)&p])
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if c%2:
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result[b*blocksize+p-1] = 1
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return "".join(list(map(str, result)))
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def decode(data, blocksize=7):
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result = []
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datasize = blocksize-blocksize.bit_length()
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data = list(map(int, data))
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if len(data) % blocksize:
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raise HammingError(f"Length of data is not a multiple of {blocksize}")
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nblocks = int(len(data)/blocksize)
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errors = 0
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for b in range(nblocks):
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pos = 0
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for i in range(blocksize.bit_length()):
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p = 1 << i
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c = sum([data[b*blocksize+j] for j in range(blocksize) if (j+1)&p])
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if c%2:
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pos |= p
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if pos != 0:
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if pos > blocksize:
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raise HammingError("Too many errors")
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return
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errors += 1
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data[b*blocksize+pos-1] = 1-data[b*blocksize+pos-1]
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for i in range(1, blocksize):
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if (i+1)&i != 0:
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result.append(data[b*blocksize+i])
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return "".join(list(map(str, result))), errors
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if __name__ == "__main__":
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#print("10011010")
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print(encode("10011010"))
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#print(decode("011100101010"))
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print(decode("00110011011010101101001010101011010101010111001100110011"))
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print(decode("01000011011010101100001010101011110101000111001100111011"))
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