pycyphal.transport.commons.crc package

Module contents

This module contains implementations of various CRC algorithms used by the transports.

32-Bit Cyclic Redundancy Codes for Internet Applications (Philip Koopman).

class pycyphal.transport.commons.crc.CRCAlgorithm

Bases: abc.ABC

Implementations are default-constructible.

abstract add(data: Union[bytes, bytearray, memoryview]) → None

Updates the value with the specified block of data.

abstract check_residue() → bool

Checks if the current state matches the algorithm-specific residue.

abstract property value: int

The current CRC value, with output XOR applied, if applicable.

abstract property value_as_bytes: bytes

The current CRC value serialized in the algorithm-specific byte order.

classmethod new(*fragments: Union[bytes, bytearray, memoryview]) → pycyphal.transport.commons.crc._base.CRCAlgorithm

A factory that creates the new instance with the value computed over the fragments.

class pycyphal.transport.commons.crc.CRC16CCITT

Bases: pycyphal.transport.commons.crc._base.CRCAlgorithm

• Name: CRC-16/CCITT-FALSE

• Initial value: 0xFFFF

• Polynomial: 0x1021

• Reverse: No

• Output XOR: 0

• Residue: 0

• Check: 0x29B1

>>> assert CRC16CCITT().value == 0xFFFF
>>> c = CRC16CCITT()
>>> c.add(b'123456')
>>> c.add(b'789')
>>> c.value
10673
>>> c.add(b'')
>>> c.value
10673
>>> c.add(c.value_as_bytes)
>>> c.value
0
>>> c.check_residue()
True

__init__() → None

add(data: Union[bytes, bytearray, memoryview]) → None

check_residue() → bool

property value: int

property value_as_bytes: bytes

class pycyphal.transport.commons.crc.CRC32C

Bases: pycyphal.transport.commons.crc._base.CRCAlgorithm

32-Bit Cyclic Redundancy Codes for Internet Applications (Philip Koopman).

CRC-32C (Castagnoli) for C++ and .NET.

• Name: CRC-32/ISCSI, CRC-32C, CRC-32/CASTAGNOLI

• Initial value: 0xFFFFFFFF

• Polynomial: 0x1EDC6F41

• Output XOR: 0xFFFFFFFF

• Residue: 0xB798B438

• Check: 0xE3069283

>>> assert CRC32C().value == 0
>>> c = CRC32C()
>>> c.add(b'123456')
>>> c.add(b'789')
>>> c.value  # 0xE3069283
3808858755
>>> c.add(b'')
>>> c.value
3808858755
>>> c.add(c.value_as_bytes)
>>> c.value  # Inverted residue
1214729159
>>> c.check_residue()
True
>>> CRC32C.new(b'123', b'', b'456789').value
3808858755

__init__() → None

add(data: Union[bytes, bytearray, memoryview]) → None

check_residue() → bool

property value: int

property value_as_bytes: bytes

class pycyphal.transport.commons.crc.CRC64WE

Bases: pycyphal.transport.commons.crc._base.CRCAlgorithm

A CRC-64/WE algorithm implementation.

• Name: CRC-64/WE

• Initial value: 0xFFFFFFFFFFFFFFFF

• Polynomial: 0x42F0E1EBA9EA3693

• Output XOR: 0xFFFFFFFFFFFFFFFF

• Residue: 0xFCACBEBD5931A992

• Check: 0x62EC59E3F1A4F00A

>>> assert CRC64WE().value == 0
>>> c = CRC64WE()
>>> c.add(b'123456')
>>> c.add(b'789')
>>> c.value  # 0x62EC59E3F1A4F00A
7128171145767219210
>>> c.add(b'')
>>> c.value
7128171145767219210
>>> c.add(c.value_as_bytes)
>>> c.value  # Inverted residue
239606959702955629
>>> c.check_residue()
True
>>> CRC64WE.new(b'123', b'', b'456789').value
7128171145767219210

__init__() → None

add(data: Union[bytes, bytearray, memoryview]) → None

check_residue() → bool

property value: int

property value_as_bytes: bytes