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bpo-47040: improve document of checksum functions (gh-31955)

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Clarifies a versionchanged note on crc32 & adler32 docs that the workaround is only needed for Python 2 and earlier.
Also cleans up an unnecessary intermediate variable in the implementation.

Authored-By: Ma Lin / animalize
Co-authored-by: Gregory P. Smith <greg@krypto.org>
This commit is contained in:
Ma Lin 2022-03-20 05:42:04 +08:00 • committed by GitHub
parent 82e9b0bb0a
commit b3f2d4c8ba
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4 changed files with 14 additions and 17 deletions
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7
Doc/library/binascii.rst
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@ -107,7 +107,7 @@ The :mod:`binascii` module defines the following functions:
.. function:: crc32(data[, value])
Compute CRC-32, the 32-bit checksum of *data*, starting with an
Compute CRC-32, the unsigned 32-bit checksum of *data*, starting with an
initial CRC of *value*. The default initial CRC is zero. The algorithm
is consistent with the ZIP file checksum. Since the algorithm is designed for
use as a checksum algorithm, it is not suitable for use as a general hash
@ -121,9 +121,8 @@ The :mod:`binascii` module defines the following functions:
.. versionchanged:: 3.0
The result is always unsigned.
To generate the same numeric value across all Python versions and
platforms, use ``crc32(data) & 0xffffffff``.
To generate the same numeric value when using Python 2 or earlier,
use ``crc32(data) & 0xffffffff``.
.. function:: b2a_hex(data[, sep[, bytes_per_sep=1]])
hexlify(data[, sep[, bytes_per_sep=1]])

14
Doc/library/zlib.rst
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@ -42,10 +42,9 @@ The available exception and functions in this module are:
for use as a general hash algorithm.
.. versionchanged:: 3.0
Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use ``adler32(data) & 0xffffffff``.
The result is always unsigned.
To generate the same numeric value when using Python 2 or earlier,
use ``adler32(data) & 0xffffffff``.
.. function:: compress(data, /, level=-1, wbits=MAX_WBITS)
@ -137,10 +136,9 @@ The available exception and functions in this module are:
for use as a general hash algorithm.
.. versionchanged:: 3.0
Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use ``crc32(data) & 0xffffffff``.
The result is always unsigned.
To generate the same numeric value when using Python 2 or earlier,
use ``crc32(data) & 0xffffffff``.
.. function:: decompress(data, /, wbits=MAX_WBITS, bufsize=DEF_BUF_SIZE)

2
Misc/NEWS.d/next/Documentation/2022-03-17-13-35-28.bpo-47040.4Dn48U.rst Normal file
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@ -0,0 +1,2 @@
Clarified the old Python versions compatiblity note of :func:`binascii.crc32` /
:func:`zlib.adler32` / :func:`zlib.crc32` functions.

8
Modules/zlibmodule.c
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@ -1436,8 +1436,6 @@ static PyObject *
zlib_crc32_impl(PyObject *module, Py_buffer *data, unsigned int value)
/*[clinic end generated code: output=63499fa20af7ea25 input=26c3ed430fa00b4c]*/
{
int signed_val;
/* Releasing the GIL for very small buffers is inefficient
and may lower performance */
if (data->len > 1024*5) {
@ -1452,12 +1450,12 @@ zlib_crc32_impl(PyObject *module, Py_buffer *data, unsigned int value)
buf += (size_t) UINT_MAX;
len -= (size_t) UINT_MAX;
}
signed_val = crc32(value, buf, (unsigned int)len);
value = crc32(value, buf, (unsigned int)len);
Py_END_ALLOW_THREADS
} else {
signed_val = crc32(value, data->buf, (unsigned int)data->len);
value = crc32(value, data->buf, (unsigned int)data->len);
}
return PyLong_FromUnsignedLong(signed_val & 0xffffffffU);
return PyLong_FromUnsignedLong(value & 0xffffffffU);
}