File size: 8,384 Bytes
27867f1 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 |
# pycrc -- parameterisable CRC calculation utility and C source code generator
#
# Copyright (c) 2006-2017 Thomas Pircher <[email protected]>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to
# deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
# sell copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
# IN THE SOFTWARE.
"""
CRC algorithms implemented in Python.
If you want to study the Python implementation of the CRC routines, then this
is a good place to start from.
The algorithms Bit by Bit, Bit by Bit Fast and Table-Driven are implemented.
This module can also be used as a library from within Python.
Examples
========
This is an example use of the different algorithms:
from pycrc.algorithms import Crc
crc = Crc(width = 16, poly = 0x8005,
reflect_in = True, xor_in = 0x0000,
reflect_out = True, xor_out = 0x0000)
print("{0:#x}".format(crc.bit_by_bit("123456789")))
print("{0:#x}".format(crc.bit_by_bit_fast("123456789")))
print("{0:#x}".format(crc.table_driven("123456789")))
"""
class Crc(object):
"""
A base class for CRC routines.
"""
# pylint: disable=too-many-instance-attributes
def __init__(self, width, poly, reflect_in, xor_in, reflect_out, xor_out, table_idx_width=None, slice_by=1):
"""The Crc constructor.
The parameters are as follows:
width
poly
reflect_in
xor_in
reflect_out
xor_out
"""
# pylint: disable=too-many-arguments
self.width = width
self.poly = poly
self.reflect_in = reflect_in
self.xor_in = xor_in
self.reflect_out = reflect_out
self.xor_out = xor_out
self.tbl_idx_width = table_idx_width
self.slice_by = slice_by
self.msb_mask = 0x1 << (self.width - 1)
self.mask = ((self.msb_mask - 1) << 1) | 1
if self.tbl_idx_width is not None:
self.tbl_width = 1 << self.tbl_idx_width
else:
self.tbl_idx_width = 8
self.tbl_width = 1 << self.tbl_idx_width
self.direct_init = self.xor_in
self.nondirect_init = self.__get_nondirect_init(self.xor_in)
if self.width < 8:
self.crc_shift = 8 - self.width
else:
self.crc_shift = 0
def __get_nondirect_init(self, init):
"""
return the non-direct init if the direct algorithm has been selected.
"""
crc = init
for dummy_i in range(self.width):
bit = crc & 0x01
if bit:
crc ^= self.poly
crc >>= 1
if bit:
crc |= self.msb_mask
return crc & self.mask
def reflect(self, data, width):
"""
reflect a data word, i.e. reverts the bit order.
"""
# pylint: disable=no-self-use
res = data & 0x01
for dummy_i in range(width - 1):
data >>= 1
res = (res << 1) | (data & 0x01)
return res
def bit_by_bit(self, in_data):
"""
Classic simple and slow CRC implementation. This function iterates bit
by bit over the augmented input message and returns the calculated CRC
value at the end.
"""
# If the input data is a string, convert to bytes.
if isinstance(in_data, str):
in_data = bytearray(in_data, 'utf-8')
reg = self.nondirect_init
for octet in in_data:
if self.reflect_in:
octet = self.reflect(octet, 8)
for i in range(8):
topbit = reg & self.msb_mask
reg = ((reg << 1) & self.mask) | ((octet >> (7 - i)) & 0x01)
if topbit:
reg ^= self.poly
for i in range(self.width):
topbit = reg & self.msb_mask
reg = ((reg << 1) & self.mask)
if topbit:
reg ^= self.poly
if self.reflect_out:
reg = self.reflect(reg, self.width)
return (reg ^ self.xor_out) & self.mask
def bit_by_bit_fast(self, in_data):
"""
This is a slightly modified version of the bit-by-bit algorithm: it
does not need to loop over the augmented bits, i.e. the Width 0-bits
wich are appended to the input message in the bit-by-bit algorithm.
"""
# If the input data is a string, convert to bytes.
if isinstance(in_data, str):
in_data = bytearray(in_data, 'utf-8')
reg = self.direct_init
for octet in in_data:
if self.reflect_in:
octet = self.reflect(octet, 8)
for i in range(8):
topbit = reg & self.msb_mask
if octet & (0x80 >> i):
topbit ^= self.msb_mask
reg <<= 1
if topbit:
reg ^= self.poly
reg &= self.mask
if self.reflect_out:
reg = self.reflect(reg, self.width)
return reg ^ self.xor_out
def gen_table(self):
"""
This function generates the CRC table used for the table_driven CRC
algorithm. The Python version cannot handle tables of an index width
other than 8. See the generated C code for tables with different sizes
instead.
"""
table_length = 1 << self.tbl_idx_width
tbl = [[0 for i in range(table_length)] for j in range(self.slice_by)]
for i in range(table_length):
reg = i
if self.reflect_in:
reg = self.reflect(reg, self.tbl_idx_width)
reg = reg << (self.width - self.tbl_idx_width + self.crc_shift)
for dummy_j in range(self.tbl_idx_width):
if reg & (self.msb_mask << self.crc_shift) != 0:
reg = (reg << 1) ^ (self.poly << self.crc_shift)
else:
reg = (reg << 1)
if self.reflect_in:
reg = self.reflect(reg >> self.crc_shift, self.width) << self.crc_shift
tbl[0][i] = (reg >> self.crc_shift) & self.mask
for j in range(1, self.slice_by):
for i in range(table_length):
tbl[j][i] = (tbl[j - 1][i] >> 8) ^ tbl[0][tbl[j - 1][i] & 0xff]
return tbl
def table_driven(self, in_data):
"""
The Standard table_driven CRC algorithm.
"""
# pylint: disable = line-too-long
# If the input data is a string, convert to bytes.
if isinstance(in_data, str):
in_data = bytearray(in_data, 'utf-8')
tbl = self.gen_table()
if not self.reflect_in:
reg = self.direct_init << self.crc_shift
for octet in in_data:
tblidx = ((reg >> (self.width - self.tbl_idx_width + self.crc_shift)) ^ octet) & 0xff
reg = ((reg << (self.tbl_idx_width - self.crc_shift)) ^
(tbl[0][tblidx] << self.crc_shift)) & (self.mask << self.crc_shift)
reg = reg >> self.crc_shift
else:
reg = self.reflect(self.direct_init, self.width)
for octet in in_data:
tblidx = (reg ^ octet) & 0xff
reg = ((reg >> self.tbl_idx_width) ^ tbl[0][tblidx]) & self.mask
reg = self.reflect(reg, self.width) & self.mask
if self.reflect_out:
reg = self.reflect(reg, self.width)
return reg ^ self.xor_out
|