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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.
#
import re
__all__ = [
"bitreverse",
"poly2int",
"int2poly",
]
def bitreverse(value, nrBits):
"""Reverse the bits in an integer.
"""
ret = 0
for _ in range(nrBits):
ret = (ret << 1) | (value & 1)
value >>= 1
return ret
def poly2int(polyString, nrBits, shiftRight=False):
"""Convert polynomial coefficient string to binary integer.
"""
polyString = polyString.lower().strip();
if polyString.startswith("0x"):
# Hex format
try:
poly = int(polyString[2:], 16)
except ValueError:
raise ValueError("Invalid polynomial coefficient format.")
else:
try:
# Decimal format
poly = int(polyString, 10)
except ValueError:
# Polynomial coefficient format
polyString, _ = re.subn(r"\s+", "", polyString)
poly = 0
try:
for bit in polyString.split("+"):
if bit.startswith("x^"):
poly |= 1 << int(bit[2:], 10)
elif bit == "x":
poly |= 1 << 1
elif bit == "1":
poly |= 1 << 0
else:
raise ValueError
except ValueError:
raise ValueError("Invalid polynomial coefficient format.")
poly &= (1 << nrBits) - 1
if shiftRight:
poly = bitreverse(poly, nrBits)
return poly
def int2poly(poly, nrBits, shiftRight=False):
"""Convert binary integer polynomial coefficient to string.
"""
poly &= (1 << nrBits) - 1
if shiftRight:
poly = bitreverse(poly, nrBits)
p = []
shift = 0
while poly:
if poly & 1:
if shift == 0:
p.append("1")
elif shift == 1:
p.append("x")
else:
p.append(f"x^{shift}")
shift += 1
poly >>= 1
p.append(f"x^{nrBits}")
return " + ".join(reversed(p))
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