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6118.2.3
by John Arbash Meinel
An 'entropy' computation. |
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# Copyright (C) 2011 Canonical Ltd
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#
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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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#
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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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#
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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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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"""Code to estimate the entropy of content"""
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import zlib |
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6118.2.6
by John Arbash Meinel
Updates to ZLibEstimator. |
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6118.2.3
by John Arbash Meinel
An 'entropy' computation. |
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class ZLibEstimator(object): |
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"""Uses zlib.compressobj to estimate compressed size."""
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6118.2.6
by John Arbash Meinel
Updates to ZLibEstimator. |
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def __init__(self, target_size, min_compression=2.0): |
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"""Create a new estimator.
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:param target_size: The desired size of the compressed content.
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:param min_compression: Estimated minimum compression. By default we
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assume that the content is 'text', which means a min compression of
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about 2:1.
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"""
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6118.2.3
by John Arbash Meinel
An 'entropy' computation. |
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self._target_size = target_size |
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self._compressor = zlib.compressobj() |
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self._uncompressed_size_added = 0 |
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self._compressed_size_added = 0 |
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self._unflushed_size_added = 0 |
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6118.2.6
by John Arbash Meinel
Updates to ZLibEstimator. |
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self._estimated_compression = 2.0 |
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6118.2.3
by John Arbash Meinel
An 'entropy' computation. |
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def add_content(self, content): |
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self._uncompressed_size_added += len(content) |
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self._unflushed_size_added += len(content) |
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z_size = len(self._compressor.compress(content)) |
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if z_size > 0: |
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6118.2.6
by John Arbash Meinel
Updates to ZLibEstimator. |
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self._record_z_len(z_size) |
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def _record_z_len(self, count): |
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# We got some compressed bytes, update the counters
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self._compressed_size_added += count |
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self._unflushed_size_added = 0 |
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# So far we've read X uncompressed bytes, and written Y compressed
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# bytes. We should have a decent estimate of the final compression.
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self._estimated_compression = (float(self._uncompressed_size_added) |
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/ self._compressed_size_added) |
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6118.2.3
by John Arbash Meinel
An 'entropy' computation. |
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def full(self): |
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"""Have we reached the target size?"""
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6118.2.6
by John Arbash Meinel
Updates to ZLibEstimator. |
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if self._unflushed_size_added: |
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remaining_size = self._target_size - self._compressed_size_added |
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# Estimate how much compressed content the unflushed data will
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# consume
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est_z_size = (self._unflushed_size_added / |
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self._estimated_compression) |
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if est_z_size >= remaining_size: |
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# We estimate we are close to remaining
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z_size = len(self._compressor.flush(zlib.Z_SYNC_FLUSH)) |
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self._record_z_len(z_size) |
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6118.2.3
by John Arbash Meinel
An 'entropy' computation. |
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return self._compressed_size_added >= self._target_size |