HBLink/RS129.py

'''
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.

Slight gratuitous modifications were made to match functionality with HBlink and DMRlink
'''

from __future__ import print_function
from binascii import b2a_hex as h

START_MASK = [0x96, 0x96, 0x96]
END_MASK = [0x99, 0x99, 0x99]
NUM_BYTES = 9
NPAR = 3;
POLY= [64, 56, 14, 1, 0, 0, 0, 0, 0, 0, 0, 0]

EXP_TABLE = (
	0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1D, 0x3A, 0x74, 0xE8, 0xCD, 0x87, 0x13, 0x26,
	0x4C, 0x98, 0x2D, 0x5A, 0xB4, 0x75, 0xEA, 0xC9, 0x8F, 0x03, 0x06, 0x0C, 0x18, 0x30, 0x60, 0xC0,
	0x9D, 0x27, 0x4E, 0x9C, 0x25, 0x4A, 0x94, 0x35, 0x6A, 0xD4, 0xB5, 0x77, 0xEE, 0xC1, 0x9F, 0x23,
	0x46, 0x8C, 0x05, 0x0A, 0x14, 0x28, 0x50, 0xA0, 0x5D, 0xBA, 0x69, 0xD2, 0xB9, 0x6F, 0xDE, 0xA1,
	0x5F, 0xBE, 0x61, 0xC2, 0x99, 0x2F, 0x5E, 0xBC, 0x65, 0xCA, 0x89, 0x0F, 0x1E, 0x3C, 0x78, 0xF0,
	0xFD, 0xE7, 0xD3, 0xBB, 0x6B, 0xD6, 0xB1, 0x7F, 0xFE, 0xE1, 0xDF, 0xA3, 0x5B, 0xB6, 0x71, 0xE2,
	0xD9, 0xAF, 0x43, 0x86, 0x11, 0x22, 0x44, 0x88, 0x0D, 0x1A, 0x34, 0x68, 0xD0, 0xBD, 0x67, 0xCE,
	0x81, 0x1F, 0x3E, 0x7C, 0xF8, 0xED, 0xC7, 0x93, 0x3B, 0x76, 0xEC, 0xC5, 0x97, 0x33, 0x66, 0xCC,
	0x85, 0x17, 0x2E, 0x5C, 0xB8, 0x6D, 0xDA, 0xA9, 0x4F, 0x9E, 0x21, 0x42, 0x84, 0x15, 0x2A, 0x54,
	0xA8, 0x4D, 0x9A, 0x29, 0x52, 0xA4, 0x55, 0xAA, 0x49, 0x92, 0x39, 0x72, 0xE4, 0xD5, 0xB7, 0x73,
	0xE6, 0xD1, 0xBF, 0x63, 0xC6, 0x91, 0x3F, 0x7E, 0xFC, 0xE5, 0xD7, 0xB3, 0x7B, 0xF6, 0xF1, 0xFF,
	0xE3, 0xDB, 0xAB, 0x4B, 0x96, 0x31, 0x62, 0xC4, 0x95, 0x37, 0x6E, 0xDC, 0xA5, 0x57, 0xAE, 0x41,
	0x82, 0x19, 0x32, 0x64, 0xC8, 0x8D, 0x07, 0x0E, 0x1C, 0x38, 0x70, 0xE0, 0xDD, 0xA7, 0x53, 0xA6,
	0x51, 0xA2, 0x59, 0xB2, 0x79, 0xF2, 0xF9, 0xEF, 0xC3, 0x9B, 0x2B, 0x56, 0xAC, 0x45, 0x8A, 0x09,
	0x12, 0x24, 0x48, 0x90, 0x3D, 0x7A, 0xF4, 0xF5, 0xF7, 0xF3, 0xFB, 0xEB, 0xCB, 0x8B, 0x0B, 0x16,
	0x2C, 0x58, 0xB0, 0x7D, 0xFA, 0xE9, 0xCF, 0x83, 0x1B, 0x36, 0x6C, 0xD8, 0xAD, 0x47, 0x8E, 0x01,
	0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1D, 0x3A, 0x74, 0xE8, 0xCD, 0x87, 0x13, 0x26, 0x4C,
	0x98, 0x2D, 0x5A, 0xB4, 0x75, 0xEA, 0xC9, 0x8F, 0x03, 0x06, 0x0C, 0x18, 0x30, 0x60, 0xC0, 0x9D,
	0x27, 0x4E, 0x9C, 0x25, 0x4A, 0x94, 0x35, 0x6A, 0xD4, 0xB5, 0x77, 0xEE, 0xC1, 0x9F, 0x23, 0x46,
	0x8C, 0x05, 0x0A, 0x14, 0x28, 0x50, 0xA0, 0x5D, 0xBA, 0x69, 0xD2, 0xB9, 0x6F, 0xDE, 0xA1, 0x5F,
	0xBE, 0x61, 0xC2, 0x99, 0x2F, 0x5E, 0xBC, 0x65, 0xCA, 0x89, 0x0F, 0x1E, 0x3C, 0x78, 0xF0, 0xFD,
	0xE7, 0xD3, 0xBB, 0x6B, 0xD6, 0xB1, 0x7F, 0xFE, 0xE1, 0xDF, 0xA3, 0x5B, 0xB6, 0x71, 0xE2, 0xD9,
	0xAF, 0x43, 0x86, 0x11, 0x22, 0x44, 0x88, 0x0D, 0x1A, 0x34, 0x68, 0xD0, 0xBD, 0x67, 0xCE, 0x81,
	0x1F, 0x3E, 0x7C, 0xF8, 0xED, 0xC7, 0x93, 0x3B, 0x76, 0xEC, 0xC5, 0x97, 0x33, 0x66, 0xCC, 0x85,
	0x17, 0x2E, 0x5C, 0xB8, 0x6D, 0xDA, 0xA9, 0x4F, 0x9E, 0x21, 0x42, 0x84, 0x15, 0x2A, 0x54, 0xA8,
	0x4D, 0x9A, 0x29, 0x52, 0xA4, 0x55, 0xAA, 0x49, 0x92, 0x39, 0x72, 0xE4, 0xD5, 0xB7, 0x73, 0xE6,
	0xD1, 0xBF, 0x63, 0xC6, 0x91, 0x3F, 0x7E, 0xFC, 0xE5, 0xD7, 0xB3, 0x7B, 0xF6, 0xF1, 0xFF, 0xE3,
	0xDB, 0xAB, 0x4B, 0x96, 0x31, 0x62, 0xC4, 0x95, 0x37, 0x6E, 0xDC, 0xA5, 0x57, 0xAE, 0x41, 0x82,
	0x19, 0x32, 0x64, 0xC8, 0x8D, 0x07, 0x0E, 0x1C, 0x38, 0x70, 0xE0, 0xDD, 0xA7, 0x53, 0xA6, 0x51,
	0xA2, 0x59, 0xB2, 0x79, 0xF2, 0xF9, 0xEF, 0xC3, 0x9B, 0x2B, 0x56, 0xAC, 0x45, 0x8A, 0x09, 0x12,
	0x24, 0x48, 0x90, 0x3D, 0x7A, 0xF4, 0xF5, 0xF7, 0xF3, 0xFB, 0xEB, 0xCB, 0x8B, 0x0B, 0x16, 0x2C,
	0x58, 0xB0, 0x7D, 0xFA, 0xE9, 0xCF, 0x83, 0x1B, 0x36, 0x6C, 0xD8, 0xAD, 0x47, 0x8E, 0x01, 0x00
    )

LOG_TABLE = (
	0x00, 0x00, 0x01, 0x19, 0x02, 0x32, 0x1A, 0xC6, 0x03, 0xDF, 0x33, 0xEE, 0x1B, 0x68, 0xC7, 0x4B,
	0x04, 0x64, 0xE0, 0x0E, 0x34, 0x8D, 0xEF, 0x81, 0x1C, 0xC1, 0x69, 0xF8, 0xC8, 0x08, 0x4C, 0x71,
	0x05, 0x8A, 0x65, 0x2F, 0xE1, 0x24, 0x0F, 0x21, 0x35, 0x93, 0x8E, 0xDA, 0xF0, 0x12, 0x82, 0x45,
	0x1D, 0xB5, 0xC2, 0x7D, 0x6A, 0x27, 0xF9, 0xB9, 0xC9, 0x9A, 0x09, 0x78, 0x4D, 0xE4, 0x72, 0xA6,
	0x06, 0xBF, 0x8B, 0x62, 0x66, 0xDD, 0x30, 0xFD, 0xE2, 0x98, 0x25, 0xB3, 0x10, 0x91, 0x22, 0x88,
	0x36, 0xD0, 0x94, 0xCE, 0x8F, 0x96, 0xDB, 0xBD, 0xF1, 0xD2, 0x13, 0x5C, 0x83, 0x38, 0x46, 0x40,
	0x1E, 0x42, 0xB6, 0xA3, 0xC3, 0x48, 0x7E, 0x6E, 0x6B, 0x3A, 0x28, 0x54, 0xFA, 0x85, 0xBA, 0x3D,
	0xCA, 0x5E, 0x9B, 0x9F, 0x0A, 0x15, 0x79, 0x2B, 0x4E, 0xD4, 0xE5, 0xAC, 0x73, 0xF3, 0xA7, 0x57,
	0x07, 0x70, 0xC0, 0xF7, 0x8C, 0x80, 0x63, 0x0D, 0x67, 0x4A, 0xDE, 0xED, 0x31, 0xC5, 0xFE, 0x18,
	0xE3, 0xA5, 0x99, 0x77, 0x26, 0xB8, 0xB4, 0x7C, 0x11, 0x44, 0x92, 0xD9, 0x23, 0x20, 0x89, 0x2E,
	0x37, 0x3F, 0xD1, 0x5B, 0x95, 0xBC, 0xCF, 0xCD, 0x90, 0x87, 0x97, 0xB2, 0xDC, 0xFC, 0xBE, 0x61,
	0xF2, 0x56, 0xD3, 0xAB, 0x14, 0x2A, 0x5D, 0x9E, 0x84, 0x3C, 0x39, 0x53, 0x47, 0x6D, 0x41, 0xA2,
	0x1F, 0x2D, 0x43, 0xD8, 0xB7, 0x7B, 0xA4, 0x76, 0xC4, 0x17, 0x49, 0xEC, 0x7F, 0x0C, 0x6F, 0xF6,
	0x6C, 0xA1, 0x3B, 0x52, 0x29, 0x9D, 0x55, 0xAA, 0xFB, 0x60, 0x86, 0xB1, 0xBB, 0xCC, 0x3E, 0x5A,
	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
    )
      
# multiplication using logarithms
def log_mult(a, b):
    if a == 0 or b == 0:
	    return 0
    x = LOG_TABLE[a]
    y = LOG_TABLE[b]
    z = EXP_TABLE[x + y]
    return z

# Reed-Solomon (12,9) encoder
def encode(_msg):
    assert len(_msg) == 9, 'RS129_encode error: Message not 9 bytes: %s' % print_hex(_msg)
    
    parity = [0x00, 0x00, 0x00]

    for i in range(NUM_BYTES):
        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[2], parity[1], parity[0]]

# Apply DMR XOR LC Header MASK
def lc_header_mask(_parity):
    xor = [0,0,0]
    for i in range(len(_parity)):
        xor[i] = _parity[i] ^ START_MASK[i]
    return xor
    
# Apply DMR XOR LC Terminator MASK
def lc_terminator_mask(_parity):
    xor = [0,0,0]
    for i in range(len(_parity)):
        xor[i] = _parity[i] ^ END_MASK[i]
    return xor

# All Inclusive function to take an LC string and provide the RS129 string to append
def lc_header_encode(_message):
    bin_message = bytearray(_message)
    parity = encode(bin_message)
    masked_parity = lc_header_mask(parity)
    return chr(masked_parity[0]) + chr(masked_parity[1]) + chr(masked_parity[2])
    
# All Inclusive function to take an LC string and provide the RS129 string to append
def lc_terminator_encode(_message):
    bin_message = bytearray(_message)
    parity = encode(bin_message)
    masked_parity = lc_terminator_mask(parity)
    return chr(masked_parity[0]) + chr(masked_parity[1]) + chr(masked_parity[2])
    
    


if __name__ == '__main__':
    # For testing the code
    def print_hex(_list):
        print('[{}]'.format(', '.join(hex(x) for x in _list)))
    
    # Validation Example
    message = '\x00\x10\x20\x00\x0c\x30\x2f\x9b\xe5'
    message = bytearray(message)
    parity_should_be = '\xda\x4d\x5a'
    print('Original Message:            {}'.format(h(message)))
    print('Masked Parity Should be:     {}'.format(h(parity_should_be)))
    
    parity = lc_header_encode(message)
    print('Calculated Masked Parity is: {}'.format(h(parity)))