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This commit is contained in:
Cort Buffington 2016-08-16 08:28:52 -05:00
parent d363e25cd5
commit 03e514ecff
1 changed files with 45 additions and 23 deletions
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64
RS129.py
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@ -1,6 +1,17 @@
'''
This file is a python translation of:
https://github.com/g4klx/MMDVMHost/blob/master/RS129.cpp
Copyright (C) 2015 by Jonathan Naylor G4KLX
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
'''
from __future__ import print_function from __future__ import print_function
MASK = [0x96, 0x96, 0x96] MASK = [0x96, 0x96, 0x96]
NUM_BYTES = 9
PARITY_BYTES = 3; PARITY_BYTES = 3;
MAXDEG = PARITY_BYTES * 2; MAXDEG = PARITY_BYTES * 2;
POLY= [64, 56, 14, 1, 0, 0, 0, 0, 0, 0, 0, 0] POLY= [64, 56, 14, 1, 0, 0, 0, 0, 0, 0, 0, 0]
@ -59,39 +70,50 @@ LOG_TABLE = [
0x4F, 0xAE, 0xD5, 0xE9, 0xE6, 0xE7, 0xAD, 0xE8, 0x74, 0xD6, 0xF4, 0xEA, 0xA8, 0x50, 0x58, 0xAF 0x4F, 0xAE, 0xD5, 0xE9, 0xE6, 0xE7, 0xAD, 0xE8, 0x74, 0xD6, 0xF4, 0xEA, 0xA8, 0x50, 0x58, 0xAF
] ]
# For testing the code
def print_hex(_list):
print('[{}]'.format(', '.join(hex(x) for x in _list)))
# multiplication using logarithms # multiplication using logarithms
def log_mult(a, b): def log_mult(a, b):
if a == 0 or b == 0: if a == 0 or b == 0:
return 0 return 0
return EXP_TABLE[LOG_TABLE[a] + LOG_TABLE[b]]; return EXP_TABLE[LOG_TABLE[a] + LOG_TABLE[b]];
def RS129_encode(msg): # Reed-Solomon (12,9) encoder
nbytes = 9 def RS129_encode(_msg):
parity = [0x00,0x00,0x00] assert len(_msg) == 9, 'RS129_encode error: Message not 9 bytes: %s' % print_hex(_msg)
for i in range(nbytes): parity = [0x00, 0x00, 0x00]
dbyte = msg[i] ^ parity[PARITY_BYTES - 1]
for j in range(PARITY_BYTES-1,0,-1): for i in range(NUM_BYTES):
parity[j] = parity[j - 1] ^ log_mult(POLY[j], dbyte) dbyte = _msg[i] ^ parity[PARITY_BYTES - 1]
parity[0] = log_mult(POLY[0], dbyte) for j in range(PARITY_BYTES-1, 0, -1):
parity[j] = parity[j - 1] ^ log_mult(POLY[j], dbyte)
parity[0] = log_mult(POLY[0], dbyte)
return parity return parity
'''
// Reed-Solomon (12,9) check
bool CRS129::check(const unsigned char* in)
{
assert(in != NULL);
unsigned char parity[4U]; # Reed-Solomon (12,9) check
encode(in, 9U, parity); def RS129_check(_msg):
assert len(_msg) == 12, 'RS129_check error: Message not 12 bytes: %s' % print_hex(_msg)
return in[9U] == parity[2U] && in[10U] == parity[1U] && in[11U] == parity[0U]; parity = RS129_encode(_msg[:9])
} return _msg[9] == parity[2] and msg[10] == parity[1] and msg[11] == parity[0];
'''
# For testing the code
def print_hex(_list):
print('[{}]'.format(', '.join(hex(x) for x in _list)))
# 00 00 00 00.00.01 00.00.02 82.65.6d # 00 00 00 00.00.01 00.00.02 82.65.6d
parity = RS129_encode((0x00,0x00,0x00,0x00,0x00,0x01,0x00,0x00,0x02))
for i in range(3): message = [0x00,0x00,0x00,0x00,0x00,0x01,0x00,0x00,0x02]
print(hex(parity[i]|MASK[i])) parity = RS129_encode(message)
print_hex(message+parity)
print(RS129_check(message+parity))