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# -*- coding: utf-8 -*-
#
# SPDX-License-Identifier: MIT
"""Common utility functions for LifeScan meters."""
from glucometerutils import exceptions
class MissingChecksum(exceptions.InvalidResponse):
"""The response misses the expected 4-digits checksum."""
def __init__(self, response):
super(MissingChecksum, self).__init__(
'Response is missing checksum: %s' % response)
class InvalidSerialNumber(exceptions.Error):
"""The serial number is not as expected."""
def __init__(self, serial_number):
super(InvalidSerialNumber, self).__init__(
'Serial number %s is invalid.' % serial_number)
class MalformedCommand(exceptions.InvalidResponse):
def __init__(self, message):
super(MalformedCommand, self).__init__(
'Malformed command: %s' % message)
def crc_ccitt(data):
# type: (bytes) -> int
"""Calculate the CRC-16-CCITT with LifeScan's common seed.
Args:
data: (bytes) the data to calculate the checksum of
Returns:
(int) The 16-bit integer value of the CRC-CCITT calculated.
This function uses the non-default 0xFFFF seed as used by multiple
LifeScan meters.
"""
crc = 0xffff
for byte in data:
crc = (crc >> 8) & 0xffff | (crc << 8) & 0xffff
crc ^= byte
crc ^= (crc & 0xff) >> 4
crc ^= (((crc << 8) & 0xffff) << 4) & 0xffff
crc ^= (crc & 0xff) << 5
return crc & 0xffff
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