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Working RS 12 9 Encoder. YAY!

This commit is contained in:
Cort Buffington 2016-09-07 16:31:52 -05:00
parent c349765cd5
commit f9392ab032
1 changed files with 32 additions and 28 deletions
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60
RS129.py
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@ -6,13 +6,17 @@ This file is a python translation of:
* 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.
Slight gratuitous modifications were made to match functionality with HBlink and DMRlink
'''
from __future__ import print_function
from binascii import b2a_hex as h
from binascii import a2b_hex as a2b
MASK = [0x96, 0x96, 0x96]
NUM_BYTES = 9
PARITY_BYTES = 3;
NPAR = 3;
POLY= [64, 56, 14, 1, 0, 0, 0, 0, 0, 0, 0, 0]
EXP_TABLE = [
@ -68,23 +72,15 @@ LOG_TABLE = [
0xCB, 0x59, 0x5F, 0xB0, 0x9C, 0xA9, 0xA0, 0x51, 0x0B, 0xF5, 0x16, 0xEB, 0x7A, 0x75, 0x2C, 0xD7,
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)))
# XOR parity bytes
def xor_parity(_parity):
_return = [0,0,0]
for i in range(3):
_return[i] = _parity[i] ^ MASK[i]
return _return
# multiplication using logarithms
def log_mult(a, b):
if a == 0 or b == 0:
return 0
return EXP_TABLE[LOG_TABLE[a] + LOG_TABLE[b]];
x = LOG_TABLE[a]
y = LOG_TABLE[b]
z = EXP_TABLE[x + y]
return z
# Reed-Solomon (12,9) encoder
def RS129_encode(_msg):
@ -93,35 +89,43 @@ def RS129_encode(_msg):
parity = [0x00, 0x00, 0x00]
for i in range(NUM_BYTES):
dbyte = _msg[i] ^ parity[PARITY_BYTES - 1]
for j in range(PARITY_BYTES-1, 0, -1):
dbyte = _msg[i] ^ parity[NPAR - 1]
for j in range(NPAR - 1, 0, -1):
parity[j] = parity[j - 1] ^ log_mult(POLY[j], dbyte)
parity[0] = log_mult(POLY[0], dbyte)
return parity
parity[0] = log_mult(POLY[0], dbyte)
return parity
# Reed-Solomon (12,9) check
def RS129_check(_msg):
assert len(_msg) == 12, 'RS129_check error: Message not 12 bytes: %s' % print_hex(_msg)
parity = RS129_encode(_msg[:9])
return _msg[9] == parity[2] and msg[10] == parity[1] and msg[11] == parity[0];
# Apply DMR XOR MASK
def xor_mask(_parity):
xor = [0,0,0]
for i in range(len(_parity)):
xor[i] = _parity[i] ^ MASK[i]
return xor
# All Inclusive function to take an LC string and provide the RS129 string to append
def DMR_RS129_LC_FEC(_message):
bin_message = bytearray(_message)
parity = RS129_encode(bin_message)
xor_parity = xor_mask(parity)
return chr(xor_parity[2]) + chr(xor_parity[1]) + chr(xor_parity[0])
# For testing the code
def print_hex(_list):
print('[{}]'.format(', '.join(hex(x) for x in _list)))
# 00 10 20 00.0c.30 2f.9b.e5 da.d4.5a
expectp = [0xda,0x4d,0x5a]
message = [0x00,0x10,0x20,0x00,0x0c,0x30,0x2f,0x9b,0xe5]
parity = RS129_encode(message)
xorparity = xor_parity(parity)
if __name__ == '__main__':
print_hex(xorparity)
print_hex(message+parity)
message = '\x00\x10\x20\x00\x0c\x30\x2f\x9b\xe5'
parity = DMR_RS129_LC_FEC(message)
print(h(parity))