72 lines
2.2 KiB
Python
72 lines
2.2 KiB
Python
# Copyright 2020 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import struct
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# NOTE: ``__config__`` **must** be the first import because it (may)
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# modify the search path used to locate shared libraries.
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import google_crc32c.__config__
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import google_crc32c._crc32c_cffi
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from google_crc32c._checksum import CommonChecksum
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def extend(crc, chunk):
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"""Update an existing CRC checksum with new chunk of data.
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Args
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crc (int): An existing CRC check sum.
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chunk (Union[bytes, List[int], Tuple[int]]): A new chunk of data.
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Intended to be a byte string or similar.
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Returns
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int: New CRC checksum computed by extending existing CRC
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with ``chunk``.
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"""
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return google_crc32c._crc32c_cffi.lib.crc32c_extend(crc, chunk, len(chunk))
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def value(chunk):
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"""Compute a CRC checksum for a chunk of data.
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Args
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chunk (Union[bytes, List[int], Tuple[int]]): A new chunk of data.
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Intended to be a byte string or similar.
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Returns
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int: New CRC checksum computed for ``chunk``.
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"""
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return google_crc32c._crc32c_cffi.lib.crc32c_value(chunk, len(chunk))
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class Checksum(CommonChecksum):
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"""Hashlib-alike helper for CRC32C operations.
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Args:
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initial_value (Optional[bytes]): the initial chunk of data from
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which the CRC32C checksum is computed. Defaults to b''.
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"""
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__slots__ = ("_crc",)
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def __init__(self, initial_value=b""):
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self._crc = value(initial_value)
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def update(self, chunk):
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"""Update the checksum with a new chunk of data.
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Args:
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chunk (Optional[bytes]): a chunk of data used to extend
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the CRC32C checksum.
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"""
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self._crc = extend(self._crc, chunk)
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