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# Copyright (C) 2005, 2006 by Canonical Ltd
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# Written by Robert Collins <robert.collins@canonical.com>
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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"""Bzrlib specific gzip tunings. We plan to feed these to the upstream gzip."""
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# make GzipFile faster:
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from gzip import U32, LOWU32, FEXTRA, FCOMMENT, FNAME, FHCRC
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# we want a \n preserved, break on \n only splitlines.
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__all__ = ["GzipFile"]
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class GzipFile(gzip.GzipFile):
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"""Knit tuned version of GzipFile.
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This is based on the following lsprof stats:
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python 2.4 stock GzipFile write:
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58971 0 5644.3090 2721.4730 gzip:193(write)
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+58971 0 1159.5530 1159.5530 +<built-in method compress>
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+176913 0 987.0320 987.0320 +<len>
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+58971 0 423.1450 423.1450 +<zlib.crc32>
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+58971 0 353.1060 353.1060 +<method 'write' of 'cStringIO.
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58971 0 4477.2590 2103.1120 bzrlib.knit:1250(write)
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+58971 0 1297.7620 1297.7620 +<built-in method compress>
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+58971 0 406.2160 406.2160 +<zlib.crc32>
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+58971 0 341.9020 341.9020 +<method 'write' of 'cStringIO.
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+58971 0 328.2670 328.2670 +<len>
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Yes, its only 1.6 seconds, but they add up.
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def _add_read_data(self, data):
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# temp var for len(data) and switch to +='s.
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self.crc = zlib.crc32(data, self.crc)
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self.extrasize += len_data
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def _read(self, size=1024):
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# various optimisations:
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# reduces lsprof count from 2500 to
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# 8337 calls in 1272, 365 internal
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if self.fileobj is None:
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raise EOFError, "Reached EOF"
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# If the _new_member flag is set, we have to
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# jump to the next member, if there is one.
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# First, check if we're at the end of the file;
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# if so, it's time to stop; no more members to read.
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next_header_bytes = self.fileobj.read(10)
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if next_header_bytes == '':
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raise EOFError, "Reached EOF"
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self._read_gzip_header(next_header_bytes)
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self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
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self._new_member = False
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# Read a chunk of data from the file
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buf = self.fileobj.read(size)
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# If the EOF has been reached, flush the decompression object
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# and mark this object as finished.
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self._add_read_data(self.decompress.flush())
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assert len(self.decompress.unused_data) >= 8, "what does flush do?"
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self._gzip_tail = self.decompress.unused_data[0:8]
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# tell the driving read() call we have stuffed all the data
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raise EOFError, 'Reached EOF'
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self._add_read_data(self.decompress.decompress(buf))
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if self.decompress.unused_data != "":
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# Ending case: we've come to the end of a member in the file,
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# so seek back to the start of the data for the next member which
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# is the length of the decompress objects unused data - the first
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# 8 bytes for the end crc and size records.
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# so seek back to the start of the unused data, finish up
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# this member, and read a new gzip header.
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# (The number of bytes to seek back is the length of the unused
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# data, minus 8 because those 8 bytes are part of this member.
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seek_length = len (self.decompress.unused_data) - 8
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# we read too much data
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self.fileobj.seek(-seek_length, 1)
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self._gzip_tail = self.decompress.unused_data[0:8]
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elif seek_length < 0:
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# we haven't read enough to check the checksum.
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assert -8 < seek_length, "too great a seek."
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buf = self.fileobj.read(-seek_length)
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self._gzip_tail = self.decompress.unused_data + buf
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self._gzip_tail = self.decompress.unused_data
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# Check the CRC and file size, and set the flag so we read
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# a new member on the next call
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self._new_member = True
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"""tuned to reduce function calls and eliminate file seeking:
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reduces lsprof count from 800 to 288
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avoid U32 call by using struct format L
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# We've read to the end of the file, so we should have 8 bytes of
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# unused data in the decompressor. If we dont, there is a corrupt file.
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# We use these 8 bytes to calculate the CRC and the recorded file size.
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# We then check the that the computed CRC and size of the
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# uncompressed data matches the stored values. Note that the size
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# stored is the true file size mod 2**32.
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assert len(self._gzip_tail) == 8, "gzip trailer is incorrect length."
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crc32, isize = struct.unpack("<LL", self._gzip_tail)
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# note that isize is unsigned - it can exceed 2GB
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if crc32 != U32(self.crc):
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raise IOError, "CRC check failed %d %d" % (crc32, U32(self.crc))
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elif isize != LOWU32(self.size):
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raise IOError, "Incorrect length of data produced"
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def _read_gzip_header(self, bytes=None):
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"""Supply bytes if the minimum header size is already read.
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:param bytes: 10 bytes of header data.
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"""starting cost: 300 in 3998
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15998 reads from 3998 calls
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bytes = self.fileobj.read(10)
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if magic != '\037\213':
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raise IOError, 'Not a gzipped file'
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method = ord(bytes[2:3])
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raise IOError, 'Unknown compression method'
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flag = ord(bytes[3:4])
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# modtime = self.fileobj.read(4) (bytes [4:8])
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# extraflag = self.fileobj.read(1) (bytes[8:9])
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# os = self.fileobj.read(1) (bytes[9:10])
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# self.fileobj.read(6)
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# Read & discard the extra field, if present
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xlen = ord(self.fileobj.read(1))
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xlen = xlen + 256*ord(self.fileobj.read(1))
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self.fileobj.read(xlen)
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# Read and discard a null-terminated string containing the filename
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s = self.fileobj.read(1)
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if not s or s=='\000':
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# Read and discard a null-terminated string containing a comment
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s = self.fileobj.read(1)
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if not s or s=='\000':
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self.fileobj.read(2) # Read & discard the 16-bit header CRC
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def readline(self, size=-1):
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"""Tuned to remove buffer length calls in _unread and...
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also removes multiple len(c) calls, inlines _unread,
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total savings - lsprof 5800 to 5300
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8176 calls to read() in 1684
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changing the min chunk size to 200 halved all the cache misses
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leading to a drop to:
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4168 call to read() in 1646
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- i.e. just reduced the function call overhead. May be worth
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if size < 0: size = sys.maxint
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readsize = min(200, size) # Read from the file in small chunks
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return "".join(bufs) # Return resulting line
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c = self.read(readsize)
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# number of bytes read
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# We set i=size to break out of the loop under two
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# conditions: 1) there's no newline, and the chunk is
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# larger than size, or 2) there is a newline, but the
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# resulting line would be longer than 'size'.
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if i==-1 and len_c > size: i=size-1
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elif size <= i: i = size -1
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if i >= 0 or c == '':
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# if i>= 0 we have a newline or have triggered the above
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# if size is not None condition.
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# if c == '' its EOF.
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bufs.append(c[:i+1]) # Add portion of last chunk
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# -- inlined self._unread --
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## self._unread(c[i+1:], len_c - i) # Push back rest of chunk
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self.extrabuf = c[i+1:] + self.extrabuf
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self.extrasize = len_c - i + self.extrasize
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self.offset -= len_c - i
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# -- end inlined self._unread --
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return ''.join(bufs) # Return resulting line
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# Append chunk to list, decrease 'size',
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readsize = min(size, readsize * 2)
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def readlines(self, sizehint=0):
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# optimise to avoid all the buffer manipulation
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# lsprof changed from:
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# 4168 calls in 5472 with 32000 calls to readline()
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# Negative numbers result in reading all the lines
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content = self.read(sizehint)
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return bzrlib.osutils.split_lines(content)
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def _unread(self, buf, len_buf=None):
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"""tuned to remove unneeded len calls.
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because this is such an inner routine in readline, and readline is
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in many inner loops, this has been inlined into readline().
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The len_buf parameter combined with the reduction in len calls dropped
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the lsprof ms count for this routine on my test data from 800 to 200 -
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self.extrabuf = buf + self.extrabuf
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self.extrasize = len_buf + self.extrasize
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self.offset -= len_buf
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def write(self, data):
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if self.mode != gzip.WRITE:
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raise IOError(errno.EBADF, "write() on read-only GzipFile object")
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if self.fileobj is None:
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raise ValueError, "write() on closed GzipFile object"
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self.size = self.size + data_len
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self.crc = zlib.crc32(data, self.crc)
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self.fileobj.write( self.compress.compress(data) )
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self.offset += data_len
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def writelines(self, lines):
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# profiling indicated a significant overhead
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# calling write for each line.
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# this batch call is a lot faster :).
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# (4 seconds to 1 seconds for the sample upgrades I was testing).
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self.write(''.join(lines))
added
removed
bzrlib/tuned_gzip.py
