blob: ac25d22e1e71a6789faeb0ab67f86acc83a69ee8 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
|
# -*- coding: utf-8 -*-
"""Common utility functions for LifeScan meters."""
__author__ = 'Diego Elio Pettenò'
__email__ = 'flameeyes@flameeyes.eu'
__copyright__ = 'Copyright © 2013, Diego Elio Pettenò'
__license__ = 'GPL v3 or later'
import ctypes
from glucometerutils import exceptions
class MissingChecksum(exceptions.InvalidResponse):
"""The response misses the expected 4-digits checksum."""
def __init__(self, response):
self.message = 'Response is missing checksum: %s' % response
class InvalidChecksum(exceptions.InvalidResponse):
def __init__(self, expected, gotten):
self.message = (
'Response checksum not matching: %04x expected, %04x gotten' %
(expected, gotten))
class InvalidSerialNumber(exceptions.Error):
"""The serial number is not as expected."""
def __init__(self, serial_number):
self.message = 'Serial number %s is invalid.' % serial_number
def calculate_checksum(bytestring):
"""Calculate the "CRC16 Sick" style checksum for LifeScan protocols.
Args:
bytestring: the string of which the checksum has to be calculated.
Returns:
A 16-bit integer that is the checksum for the input.
Credits for this code go to Christian Navalici, who implemented it in his
library at https://github.com/cristianav/PyCRC/ .
"""
crcValue = 0x0000
prev_c = 0x0000
for idx, c in enumerate(bytestring):
short_c = 0x00ff & c
idx_previous = idx - 1
short_p = ( 0x00ff & prev_c) << 8;
if ( crcValue & 0x8000 ):
crcValue = ctypes.c_ushort(crcValue << 1).value ^ 0x8005
else:
crcValue = ctypes.c_ushort(crcValue << 1).value
crcValue &= 0xffff
crcValue ^= ( short_c | short_p )
prev_c = short_c
# After processing, the one's complement of the CRC is calcluated and the
# two bytes of the CRC are swapped.
low_byte = (crcValue & 0xff00) >> 8
high_byte = (crcValue & 0x00ff) << 8
crcValue = low_byte | high_byte;
return crcValue
|
