_Crc64Calculator._construct_lookup_table() - Code Metrics - sjwood/pydvdid - Measure and Improve Code Quality continuously with Scrutinizer

_Crc64Calculator._construct_lookup_table() A
last analyzed 2018-01-25 21:37 UTC

↳ Parent: _Crc64Calculator

Complexity

Conditions

Size

Total Lines

Duplication

Lines	0
Ratio	0 %

Importance

Changes	1
Bugs	0	Features	0

Metric	Value
cc	4
c	1
b	0
f	0
dl	0
loc	18
rs	9.2

"""Implements the _Crc64Calculator class.
"""


from __future__ import absolute_import
from .crc64result import Crc64Result


class _Crc64Calculator(object):
    """Implements a class that calculates a 64-bit Cyclic Redundancy Check checksum.

       Class initialiser requires a polynomial to seed the construction of a lookup table and an
       optional initial XOR value.
    """

    def __init__(self, polynomial, initial_xor=0xffffffffffffffff):
        self._construct_lookup_table(polynomial)
        self._crc64 = initial_xor


    @property
    def crc64(self):
        """Returns the current CRC-64.
        """

        return Crc64Result(self._crc64)


    def update(self, content):
        """Enumerates the bytes of the supplied bytearray and updates the CRC-64.
           No return value.
        """

        for byte in content:
            self._crc64 = (self._crc64 >> 8) ^ self._lookup_table[(self._crc64 & 0xff) ^ byte]


    def _construct_lookup_table(self, polynomial):
        """Precomputes a CRC-64 lookup table seeded from the supplied polynomial.
           No return value.
        """

        self._lookup_table = []

        for i in range(0, 256):
            lookup_value = i

            for _ in range(0, 8):
                if lookup_value & 0x1 == 0x1:
                    lookup_value = (lookup_value >> 1) ^ polynomial

                else:
                    lookup_value = lookup_value >> 1

            self._lookup_table.append(lookup_value)


1			"""Implements the _Crc64Calculator class.
2			"""
3
4
5			from __future__ import absolute_import
6			from .crc64result import Crc64Result
7
8
9			class _Crc64Calculator(object):
10			"""Implements a class that calculates a 64-bit Cyclic Redundancy Check checksum.
11
12			Class initialiser requires a polynomial to seed the construction of a lookup table and an
13			optional initial XOR value.
14			"""
15
16			def __init__(self, polynomial, initial_xor=0xffffffffffffffff):
17			self._construct_lookup_table(polynomial)
18			self._crc64 = initial_xor
19
20
21			@property
22			def crc64(self):
23			"""Returns the current CRC-64.
24			"""
25
26			return Crc64Result(self._crc64)
27
28
29			def update(self, content):
30			"""Enumerates the bytes of the supplied bytearray and updates the CRC-64.
31			No return value.
32			"""
33
34			for byte in content:
35			self._crc64 = (self._crc64 >> 8) ^ self._lookup_table[(self._crc64 & 0xff) ^ byte]
36
37
38			def _construct_lookup_table(self, polynomial):
39			"""Precomputes a CRC-64 lookup table seeded from the supplied polynomial.
40			No return value.
41			"""
42
43			self._lookup_table = []
44
45			for i in range(0, 256):
46			lookup_value = i
47
48			for _ in range(0, 8):
49			if lookup_value & 0x1 == 0x1:
50			lookup_value = (lookup_value >> 1) ^ polynomial
51
52			else:
53			lookup_value = lookup_value >> 1
54
55			self._lookup_table.append(lookup_value)
56

sjwood / pydvdid

_Crc64Calculator._construct_lookup_table() A last analyzed 2018-01-25 21:37 UTC

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_Crc64Calculator._construct_lookup_table() A
last analyzed 2018-01-25 21:37 UTC