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#!/usr/bin/env python3
# vim: ts=8 sw=8 noexpandtab
#
# CRC code generator
#
# Copyright (c) 2019 Michael Buesch <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",
]
class CrcReference(object):
"""Generic CRC reference implementation.
"""
@classmethod
def crc(cls, crc, data, polynomial, nrBits, shiftRight):
mask = (1 << nrBits) - 1
msb = 1 << (nrBits - 1)
lsb = 1
if shiftRight:
tmp = (crc ^ data) & 0xFF
for i in range(8):
if tmp & lsb:
tmp = ((tmp >> 1) ^ polynomial) & mask
else:
tmp = (tmp >> 1) & mask
crc = ((crc >> 8) ^ tmp) & mask
else:
tmp = (crc ^ (data << (nrBits - 8))) & mask
for i in range(8):
if tmp & msb:
tmp = ((tmp << 1) ^ polynomial) & mask
else:
tmp = (tmp << 1) & mask
crc = tmp
return crc
@classmethod
def crcBlock(cls, crc, data, polynomial, nrBits, shiftRight, preFlip, postFlip):
mask = (1 << nrBits) - 1
if preFlip:
crc ^= mask
for b in data:
crc = cls.crc(crc, b, polynomial, nrBits, shiftRight)
if postFlip:
crc ^= mask
return crc
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