diff -r 94a4980695f8 -r 729082bb9938 mercurial/revlogutils/constants.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/revlogutils/constants.py	Thu Aug 16 02:08:13 2018 +0200
@@ -0,0 +1,46 @@
+# revlogdeltas.py - constant used for revlog logic
+#
+# Copyright 2005-2007 Matt Mackall <mpm@selenic.com>
+# Copyright 2018 Octobus <contact@octobus.net>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""Helper class to compute deltas stored inside revlogs"""
+
+from __future__ import absolute_import
+
+from .. import (
+    util,
+)
+
+# revlog header flags
+REVLOGV0 = 0
+REVLOGV1 = 1
+# Dummy value until file format is finalized.
+# Reminder: change the bounds check in revlog.__init__ when this is changed.
+REVLOGV2 = 0xDEAD
+FLAG_INLINE_DATA = (1 << 16)
+FLAG_GENERALDELTA = (1 << 17)
+REVLOG_DEFAULT_FLAGS = FLAG_INLINE_DATA
+REVLOG_DEFAULT_FORMAT = REVLOGV1
+REVLOG_DEFAULT_VERSION = REVLOG_DEFAULT_FORMAT | REVLOG_DEFAULT_FLAGS
+REVLOGV1_FLAGS = FLAG_INLINE_DATA | FLAG_GENERALDELTA
+REVLOGV2_FLAGS = REVLOGV1_FLAGS
+
+# revlog index flags
+REVIDX_ISCENSORED = (1 << 15) # revision has censor metadata, must be verified
+REVIDX_ELLIPSIS = (1 << 14) # revision hash does not match data (narrowhg)
+REVIDX_EXTSTORED = (1 << 13) # revision data is stored externally
+REVIDX_DEFAULT_FLAGS = 0
+# stable order in which flags need to be processed and their processors applied
+REVIDX_FLAGS_ORDER = [
+    REVIDX_ISCENSORED,
+    REVIDX_ELLIPSIS,
+    REVIDX_EXTSTORED,
+]
+REVIDX_KNOWN_FLAGS = util.bitsfrom(REVIDX_FLAGS_ORDER)
+# bitmark for flags that could cause rawdata content change
+REVIDX_RAWTEXT_CHANGING_FLAGS = REVIDX_ISCENSORED | REVIDX_EXTSTORED
+
+# maximum <delta-chain-data>/<revision-text-length> ratio
+LIMIT_DELTA2TEXT = 2