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Issue #22341: Merge CRC doc from 3.5

This commit is contained in:
Martin Panter 2015-12-11 05:41:48 +00:00
parent 8c0b5b998a b82032f935
commit 70fe09bc67
6 changed files with 39 additions and 58 deletions
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23
Doc/library/binascii.rst
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@ -115,15 +115,16 @@ The :mod:`binascii` module defines the following functions:
possibly the last fragment).
.. function:: crc_hqx(data, crc)
.. function:: crc_hqx(data, value)
Compute the binhex4 crc value of *data*, starting with an initial *crc* and
returning the result.
Compute the binhex4 crc value of *data*, starting with *value* as the
initial crc, and return the result.
.. function:: crc32(data[, crc])
.. function:: crc32(data[, value])
Compute CRC-32, the 32-bit checksum of data, starting with an initial crc. This
Compute CRC-32, the 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
algorithm. Use as follows::
@ -131,15 +132,13 @@ The :mod:`binascii` module defines the following functions:
print(binascii.crc32(b"hello world"))
# Or, in two pieces:
crc = binascii.crc32(b"hello")
crc = binascii.crc32(b" world", crc) & 0xffffffff
crc = binascii.crc32(b" world", crc)
print('crc32 = {:#010x}'.format(crc))
.. note::
To generate the same numeric value across all Python versions and
platforms use crc32(data) & 0xffffffff. If you are only using
the checksum in packed binary format this is not necessary as the
return value is the correct 32bit binary representation
regardless of sign.
.. versionchanged:: 3.0
The result is always unsigned.
To generate the same numeric value across all Python versions and
platforms, use ``crc32(data) & 0xffffffff``.
.. function:: b2a_hex(data)

37
Doc/library/zlib.rst
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@ -31,22 +31,19 @@ The available exception and functions in this module are:
.. function:: adler32(data[, value])
Computes an Adler-32 checksum of *data*. (An Adler-32 checksum is almost as
reliable as a CRC32 but can be computed much more quickly.) If *value* is
present, it is used as the starting value of the checksum; otherwise, a fixed
default value is used. This allows computing a running checksum over the
reliable as a CRC32 but can be computed much more quickly.) The result
is an unsigned 32-bit integer. If *value* is present, it is used as
the starting value of the checksum; otherwise, a default value of 1
is used. Passing in *value* allows computing a running checksum over the
concatenation of several inputs. The algorithm is not cryptographically
strong, and should not be used for authentication or digital signatures. Since
the algorithm is designed for use as a checksum algorithm, it is not suitable
for use as a general hash algorithm.
Always returns an unsigned 32-bit integer.
.. note::
To generate the same numeric value across all Python versions and
platforms use adler32(data) & 0xffffffff. If you are only using
the checksum in packed binary format this is not necessary as the
return value is the correct 32bit binary representation
regardless of sign.
.. versionchanged:: 3.0
Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use ``adler32(data) & 0xffffffff``.
.. function:: compress(data[, level])
@ -97,23 +94,19 @@ The available exception and functions in this module are:
single: Cyclic Redundancy Check
single: checksum; Cyclic Redundancy Check
Computes a CRC (Cyclic Redundancy Check) checksum of *data*. If *value* is
present, it is used as the starting value of the checksum; otherwise, a fixed
default value is used. This allows computing a running checksum over the
Computes a CRC (Cyclic Redundancy Check) checksum of *data*. The
result is an unsigned 32-bit integer. If *value* is present, it is used
as the starting value of the checksum; otherwise, a default value of 0
is used. Passing in *value* allows computing a running checksum over the
concatenation of several inputs. The algorithm is not cryptographically
strong, and should not be used for authentication or digital signatures. Since
the algorithm is designed for use as a checksum algorithm, it is not suitable
for use as a general hash algorithm.
Always returns an unsigned 32-bit integer.
.. note::
.. versionchanged:: 3.0
Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use ``crc32(data) & 0xffffffff``. If you are only using
the checksum in packed binary format this is not necessary as the
return value is the correct 32-bit binary representation
regardless of sign.
platforms, use ``crc32(data) & 0xffffffff``.
.. function:: decompress(data[, wbits[, bufsize]])

8
Lib/gzip.py
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@ -210,7 +210,7 @@ class GzipFile(_compression.BaseStream):
def _init_write(self, filename):
self.name = filename
self.crc = zlib.crc32(b"") & 0xffffffff
self.crc = zlib.crc32(b"")
self.size = 0
self.writebuf = []
self.bufsize = 0
@ -261,7 +261,7 @@ class GzipFile(_compression.BaseStream):
if length > 0:
self.fileobj.write(self.compress.compress(data))
self.size += length
self.crc = zlib.crc32(data, self.crc) & 0xffffffff
self.crc = zlib.crc32(data, self.crc)
self.offset += length
return length
@ -381,7 +381,7 @@ class _GzipReader(_compression.DecompressReader):
self._last_mtime = None
def _init_read(self):
self._crc = zlib.crc32(b"") & 0xffffffff
self._crc = zlib.crc32(b"")
self._stream_size = 0 # Decompressed size of unconcatenated stream
def _read_exact(self, n):
@ -485,7 +485,7 @@ class _GzipReader(_compression.DecompressReader):
return uncompress
def _add_read_data(self, data):
self._crc = zlib.crc32(data, self._crc) & 0xffffffff
self._crc = zlib.crc32(data, self._crc)
self._stream_size = self._stream_size + len(data)
def _read_eof(self):

8
Lib/tarfile.py
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@ -459,13 +459,7 @@ class _Stream:
self.fileobj.write(self.buf)
self.buf = b""
if self.comptype == "gz":
# The native zlib crc is an unsigned 32-bit integer, but
# the Python wrapper implicitly casts that to a signed C
# long. So, on a 32-bit box self.crc may "look negative",
# while the same crc on a 64-bit box may "look positive".
# To avoid irksome warnings from the `struct` module, force
# it to look positive on all boxes.
self.fileobj.write(struct.pack("<L", self.crc & 0xffffffff))
self.fileobj.write(struct.pack("<L", self.crc))
self.fileobj.write(struct.pack("<L", self.pos & 0xffffFFFF))
finally:
if not self._extfileobj:

13
Lib/test/test_zlib.py
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@ -47,16 +47,11 @@ class ChecksumTestCase(unittest.TestCase):
self.assertEqual(zlib.adler32(b"", 1), 1)
self.assertEqual(zlib.adler32(b"", 432), 432)
def assertEqual32(self, seen, expected):
# 32-bit values masked -- checksums on 32- vs 64- bit machines
# This is important if bit 31 (0x08000000L) is set.
self.assertEqual(seen & 0x0FFFFFFFF, expected & 0x0FFFFFFFF)
def test_penguins(self):
self.assertEqual32(zlib.crc32(b"penguin", 0), 0x0e5c1a120)
self.assertEqual32(zlib.crc32(b"penguin", 1), 0x43b6aa94)
self.assertEqual32(zlib.adler32(b"penguin", 0), 0x0bcf02f6)
self.assertEqual32(zlib.adler32(b"penguin", 1), 0x0bd602f7)
self.assertEqual(zlib.crc32(b"penguin", 0), 0x0e5c1a120)
self.assertEqual(zlib.crc32(b"penguin", 1), 0x43b6aa94)
self.assertEqual(zlib.adler32(b"penguin", 0), 0x0bcf02f6)
self.assertEqual(zlib.adler32(b"penguin", 1), 0x0bd602f7)
self.assertEqual(zlib.crc32(b"penguin"), zlib.crc32(b"penguin", 0))
self.assertEqual(zlib.adler32(b"penguin"),zlib.adler32(b"penguin",1))

8
Lib/zipfile.py
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@ -734,7 +734,7 @@ class ZipExtFile(io.BufferedIOBase):
if hasattr(zipinfo, 'CRC'):
self._expected_crc = zipinfo.CRC
self._running_crc = crc32(b'') & 0xffffffff
self._running_crc = crc32(b'')
else:
self._expected_crc = None
@ -856,7 +856,7 @@ class ZipExtFile(io.BufferedIOBase):
if self._expected_crc is None:
# No need to compute the CRC if we don't have a reference value
return
self._running_crc = crc32(newdata, self._running_crc) & 0xffffffff
self._running_crc = crc32(newdata, self._running_crc)
# Check the CRC if we're at the end of the file
if self._eof and self._running_crc != self._expected_crc:
raise BadZipFile("Bad CRC-32 for file %r" % self.name)
@ -1492,7 +1492,7 @@ class ZipFile:
if not buf:
break
file_size = file_size + len(buf)
CRC = crc32(buf, CRC) & 0xffffffff
CRC = crc32(buf, CRC)
if cmpr:
buf = cmpr.compress(buf)
compress_size = compress_size + len(buf)
@ -1567,7 +1567,7 @@ class ZipFile:
self._writecheck(zinfo)
self._didModify = True
zinfo.CRC = crc32(data) & 0xffffffff # CRC-32 checksum
zinfo.CRC = crc32(data) # CRC-32 checksum
co = _get_compressor(zinfo.compress_type)
if co:
data = co.compress(data) + co.flush()