HBLink/hamming.py

136 lines
6.3 KiB
Python
Executable File

#!/usr/bin/env python
#
# This work is licensed under the Creative Attribution-NonCommercial-ShareAlike
# 3.0 Unported License.To view a copy of this license, visit
# http://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to
# Creative Commons, 444 Castro Street, Suite 900, Mountain View,
# California, 94041, USA.
from __future__ import print_function
from bitarray import bitarray
# Does anybody read this stuff? There's a PEP somewhere that says I should do this.
__author__ = 'Cortney T. Buffington, N0MJS'
__copyright__ = 'Copyright (c) 2016 Cortney T. Buffington, N0MJS and the K0USY Group'
__credits__ = 'Jonathan Naylor, G4KLX'
__license__ = 'Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported'
__maintainer__ = 'Cort Buffington, N0MJS'
__email__ = 'n0mjs@me.com'
#------------------------------------------------------------------------------
# Hamming 15,11,3 routines
#------------------------------------------------------------------------------
# ENCODER- returns a bitarray object containing the hamming checksums
def enc_hamming_15113(_data):
csum = bitarray(4)
csum[0] = _data[0] ^ _data[1] ^ _data[2] ^ _data[3] ^ _data[5] ^ _data[7] ^ _data[8]
csum[1] = _data[1] ^ _data[2] ^ _data[3] ^ _data[4] ^ _data[6] ^ _data[8] ^ _data[9]
csum[2] = _data[2] ^ _data[3] ^ _data[4] ^ _data[5] ^ _data[7] ^ _data[9] ^ _data[10]
csum[3] = _data[0] ^ _data[1] ^ _data[2] ^ _data[4] ^ _data[6] ^ _data[7] ^ _data[10]
return csum
# DECODER - Returns a tuple of (decoded data, True if an error was corrected)
def dec_hamming_15113(_data):
chk0 = _data[0] ^ _data[1] ^ _data[2] ^ _data[3] ^ _data[5] ^ _data[7] ^ _data[8]
chk1 = _data[1] ^ _data[2] ^ _data[3] ^ _data[4] ^ _data[6] ^ _data[8] ^ _data[9]
chk2 = _data[2] ^ _data[3] ^ _data[4] ^ _data[5] ^ _data[7] ^ _data[9] ^ _data[10]
chk3 = _data[0] ^ _data[1] ^ _data[2] ^ _data[4] ^ _data[6] ^ _data[7] ^ _data[10]
n = 0
error = False
n |= 0x01 if chk0 != _data[11] else 0x00
n |= 0x02 if chk1 != _data[12] else 0x00
n |= 0x04 if chk2 != _data[13] else 0x00
n |= 0x08 if chk3 != _data[14] else 0x00
if n == 0x01: _data[11] = not _data[11]; return (_data, True)
if n == 0x02: _data[12] = not _data[12]; return (_data, True)
if n == 0x04: _data[13] = not _data[13]; return (_data, True)
if n == 0x08: _data[14] = not _data[14]; return (_data, True)
if n == 0x0f: _data[0] = not _data[0]; return (_data, True)
if n == 0x07: _data[1] = not _data[1]; return (_data, True)
if n == 0x0b: _data[2] = not _data[2]; return (_data, True)
if n == 0x03: _data[3] = not _data[3]; return (_data, True)
if n == 0x0d: _data[4] = not _data[4]; return (_data, True)
if n == 0x05: _data[5] = not _data[5]; return (_data, True)
if n == 0x09: _data[6] = not _data[6]; return (_data, True)
if n == 0x0e: _data[7] = not _data[7]; return (_data, True)
if n == 0x06: _data[8] = not _data[8]; return (_data, True)
if n == 0x0a: _data[9] = not _data[9]; return (_data, True)
if n == 0x0c: _data[10] = not _data[10]; return (_data, True)
return (_data, False)
#------------------------------------------------------------------------------
# Hamming 13,9,3 routines
#------------------------------------------------------------------------------
# ENCODER - returns a bitarray object containing the hamming checksums
def enc_hamming_1393(_data):
csum = bitarray(4)
csum[0] = _data[0] ^ _data[1] ^ _data[3] ^ _data[5] ^ _data[6]
csum[1] = _data[0] ^ _data[1] ^ _data[2] ^ _data[4] ^ _data[6] ^ _data[7]
csum[2] = _data[0] ^ _data[1] ^ _data[2] ^ _data[3] ^ _data[5] ^ _data[7] ^ _data[8]
csum[3] = _data[0] ^ _data[2] ^ _data[4] ^ _data[5] ^ _data[8]
return csum
# DECODER - Returns a tuple of (decoded data, True if an error was corrected)
def dec_hamming_1393(_data):
chk0 = _data[0] ^ _data[1] ^ _data[3] ^ _data[5] ^ _data[6]
chk1 = _data[0] ^ _data[1] ^ _data[2] ^ _data[4] ^ _data[6] ^ _data[7]
chk2 = _data[0] ^ _data[1] ^ _data[2] ^ _data[3] ^ _data[5] ^ _data[7] ^ _data[8]
chk3 = _data[0] ^ _data[2] ^ _data[4] ^ _data[5] ^ _data[8]
n = 0
error = False
n |= 0x01 if chk0 != _data[9] else 0x00
n |= 0x02 if chk1 != _data[10] else 0x00
n |= 0x04 if chk2 != _data[11] else 0x00
n |= 0x08 if chk3 != _data[12] else 0x00
if n == 0x01: _data[9] = not _data[9]; return (_data, True)
if n == 0x02: _data[10] = not _data[10]; return (_data, True)
if n == 0x04: _data[11] = not _data[11]; return (_data, True)
if n == 0x08: _data[12] = not _data[12]; return (_data, True)
if n == 0x0f: _data[0] = not _data[0]; return (_data, True)
if n == 0x07: _data[1] = not _data[1]; return (_data, True)
if n == 0x0b: _data[2] = not _data[2]; return (_data, True)
if n == 0x03: _data[3] = not _data[3]; return (_data, True)
if n == 0x0d: _data[4] = not _data[4]; return (_data, True)
if n == 0x05: _data[5] = not _data[5]; return (_data, True)
if n == 0x09: _data[6] = not _data[6]; return (_data, True)
if n == 0x0e: _data[7] = not _data[7]; return (_data, True)
if n == 0x06: _data[8] = not _data[8]; return (_data, True)
return (_data, False)
#------------------------------------------------------------------------------
# Used to execute the module directly to run built-in tests
#------------------------------------------------------------------------------
if __name__ == '__main__':
# Validation Example
raw_data = '\x44\x4d\x52\x44\x00\x2f\x9b\xe5\x00\x0c\x30\x00\x04\xc2\xc4\xa1\xa1\x99\x48\x6e\x2b\x60\x04\x10\x1f\x84\x2d\xd0\x0d\xf0\x7d\x41\x04\x6d\xff\x57\xd7\x5d\xf5\xde\x30\x15\x2e\x20\x70\xb2\x0f\x80\x3f\x88\xc6\x95\xe2\x00\x00'
raw_data = raw_data[20:53]
data = bitarray(endian='big')
data.frombytes('raw_data')
data = data[4:]
print(data[0:11], data[11:15])
print(dec_hamming_15113(data[0:15])[0][0:11], dec_hamming_15113(data[0:15])[0][11:15], dec_hamming_15113(data[0:15])[1])
print(enc_hamming_15113(data[0:11]))
print()
print(data[0:9], data[9:13])
print(dec_hamming_1393(data[0:13])[0][0:9], dec_hamming_1393(data[0:13])[0][9:13], dec_hamming_15113(data[0:15])[1])
print(enc_hamming_1393(data[0:9]))