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# vim: ts=8 sw=8 noexpandtab
#
# CRC code generator
#
# Copyright (c) 2019-2023 Michael Büsch <m@bues.ch>
#
# 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.
#
# 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
#
__all__ = [
"CrcReference",
]
from typing import Iterable
class CrcReference:
"""Generic CRC reference implementation.
"""
@classmethod
def crc(cls,
crc: int,
data: int,
polynomial: int,
nrCrcBits: int,
nrDataBits: int = 8,
shiftRight: bool = False):
crcMask = (1 << nrCrcBits) - 1
msb = 1 << (nrCrcBits - 1)
lsb = 1
if shiftRight:
for i in range(nrDataBits):
crc ^= data & 1
data >>= 1
if crc & lsb:
crc = ((crc >> 1) ^ polynomial) & crcMask
else:
crc = (crc >> 1) & crcMask
else:
for i in range(nrDataBits):
crc ^= ((data >> (nrDataBits - 1)) & 1) << (nrCrcBits - 1)
data <<= 1
if crc & msb:
crc = ((crc << 1) ^ polynomial) & crcMask
else:
crc = (crc << 1) & crcMask
return crc
@classmethod
def crcBlock(cls,
crc: int,
data: Iterable,
polynomial: int,
nrCrcBits: int,
nrDataBits: int = 8,
shiftRight: bool = False,
preFlip: bool = False,
postFlip: bool = False):
crcMask = (1 << nrCrcBits) - 1
if preFlip:
crc ^= crcMask
for b in data:
crc = cls.crc(crc=crc,
data=b,
polynomial=polynomial,
nrCrcBits=nrCrcBits,
nrDataBits=nrDataBits,
shiftRight=shiftRight)
if postFlip:
crc ^= crcMask
return crc
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