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from __future__ import annotations
from typing import TYPE_CHECKING
from ._crc32c import crc32c
if TYPE_CHECKING:
from typing_extensions import Buffer, Self
class CRC32CHash:
"""Wrapper class for crc32c. Tries to conform to the interface of `hashlib` classes."""
@property
def digest_size(self) -> int:
"""
The size of the resulting hash in bytes.
"""
return 4
@property
def block_size(self) -> int:
"""
The internal block size of the hash algorithm in bytes.
"""
return 1
@property
def name(self) -> str:
"""
The canonical name of this hash,
"""
return "crc32c"
@property
def checksum(self) -> int:
"""
The checksum calculated so far. Not part of the hashlib interface.
"""
return self._checksum
def __init__(self, data: Buffer = b"", gil_release_mode: int = -1) -> None:
"""
Initialise the hash object with an optional bytes-like object.
Uses the given GIL release mode on each checksum calculation.
"""
self._checksum = crc32c(data, gil_release_mode=gil_release_mode)
self._gil_release_mode = gil_release_mode
def update(self, data: Buffer) -> None:
"""
Update the hash object with the bytes-like object.
Repeated calls are equivalent to a single call with the concatenation of all the arguments:
m.update(a); m.update(b) is equivalent to m.update(a+b).
"""
self._checksum = crc32c(
data, self._checksum, gil_release_mode=self._gil_release_mode
)
def digest(self) -> bytes:
"""
Return the digest of the data passed to the update() method so far.
This is a bytes object of size digest_size which may contain bytes in the whole range from 0 to 255.
"""
return self._checksum.to_bytes(4, "big")
def hexdigest(self) -> str:
"""
Like digest() except the digest is returned as a string object of double length,
containing only hexadecimal digits.
This may be used to exchange the value safely in email or other non-binary environments.
"""
return self.digest().hex()
def copy(self) -> Self:
"""
Return a copy (“clone”) of the hash object. This can be used to efficiently compute
the digests of data sharing a common initial substring.
"""
res = type(self)()
res._checksum = self._checksum
res._gil_release_mode = self._gil_release_mode
return res