1 files changed, 70 insertions, 0 deletions
diff --git a/bzrlib/estimate_compressed_size.py b/bzrlib/estimate_compressed_size.py
new file mode 100644
index 0000000..39262af
--- /dev/null
+++ b/bzrlib/estimate_compressed_size.py
@@ -0,0 +1,70 @@
+# Copyright (C) 2011 Canonical Ltd
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+"""Code to estimate the entropy of content"""
+
+from __future__ import absolute_import
+
+import zlib
+
+
+class ZLibEstimator(object):
+    """Uses zlib.compressobj to estimate compressed size."""
+
+    def __init__(self, target_size, min_compression=2.0):
+        """Create a new estimator.
+
+        :param target_size: The desired size of the compressed content.
+        :param min_compression: Estimated minimum compression. By default we
+            assume that the content is 'text', which means a min compression of
+            about 2:1.
+        """
+        self._target_size = target_size
+        self._compressor = zlib.compressobj()
+        self._uncompressed_size_added = 0
+        self._compressed_size_added = 0
+        self._unflushed_size_added = 0
+        self._estimated_compression = 2.0
+
+    def add_content(self, content):
+        self._uncompressed_size_added += len(content)
+        self._unflushed_size_added += len(content)
+        z_size = len(self._compressor.compress(content))
+        if z_size > 0:
+            self._record_z_len(z_size)
+
+    def _record_z_len(self, count):
+        # We got some compressed bytes, update the counters
+        self._compressed_size_added += count
+        self._unflushed_size_added = 0
+        # So far we've read X uncompressed bytes, and written Y compressed
+        # bytes. We should have a decent estimate of the final compression.
+        self._estimated_compression = (float(self._uncompressed_size_added)
+            / self._compressed_size_added)
+
+    def full(self):
+        """Have we reached the target size?"""
+        if self._unflushed_size_added:
+            remaining_size = self._target_size - self._compressed_size_added
+            # Estimate how much compressed content the unflushed data will
+            # consume
+            est_z_size = (self._unflushed_size_added /
+                          self._estimated_compression)
+            if est_z_size >= remaining_size:
+                # We estimate we are close to remaining
+                z_size = len(self._compressor.flush(zlib.Z_SYNC_FLUSH))
+                self._record_z_len(z_size)
+        return self._compressed_size_added >= self._target_size