########################################################################################
#
# Author: Miika Nissi
# Copyright 2023-2023 Miika Nissi (https://miikanissi.com)
#
# This file is part of zebrafy
# (see https://github.com/miikanissi/zebrafy).
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
########################################################################################
# 1. Standard library imports:
import operator
# 2. Known third party imports:
# 3. Local imports in the relative form:
[docs]
class CRC:
"""
Utility class to calculate CRC-16-CCITT algorithm across the received data bytes.
CRC-16-CCITT polynomial representation: x^{16} + x^{12} + x^5 + 1
:param data_bytes: Bytes object for which to calculate CRC
:param poly: Reversed polynomial representation for CRC-16-CCITT calculation, \
defaults to ``0x8408``
"""
def __init__(self, data_bytes: bytes, poly: int = None):
self.data_bytes = data_bytes
if poly is None:
poly = 0x8408
self.poly = poly
data_bytes = property(operator.attrgetter("_data_bytes"))
@data_bytes.setter
def data_bytes(self, d):
if d is None:
raise ValueError("Bytes data cannot be empty.")
if not isinstance(d, bytes):
raise TypeError(
f"Bytes data must be a valid bytes object. {type(d)} was given."
)
self._data_bytes = d
poly = property(operator.attrgetter("_poly"))
@poly.setter
def poly(self, p):
if p is None:
raise ValueError("Polynomial cannot be empty.")
if not isinstance(p, int):
raise TypeError(f"Polynomial must be a valid integer. {type(p)} was given.")
self._poly = p
def _get_crc16_ccitt(self) -> int:
"""
Calculate CRC-16-CCITT Algorithm.
:returns: CRC-16-CCITT
"""
data = bytearray(self._data_bytes)
crc = 0xFFFF
for b in data:
cur_byte = 0xFF & b
for _ in range(0, 8):
if (crc & 0x0001) ^ (cur_byte & 0x0001):
crc = (crc >> 1) ^ self._poly
else:
crc >>= 1
cur_byte >>= 1
crc = ~crc & 0xFFFF
crc = (crc << 8) | ((crc >> 8) & 0xFF)
return crc & 0xFFFF
[docs]
def get_crc_hex_string(self) -> str:
"""
Get CRC-16-CCITT as four digit zero padding hexadecimal string.
:returns: CRC-16-CCITT as four digit zero padding hexadecimal string
"""
return f"{self._get_crc16_ccitt():04X}"