From 2ff0cbe12512191f7d15e11c603bb8858df22976 Mon Sep 17 00:00:00 2001
From: Durham Goode <durham@fb.com>
Date: Sun, 30 Aug 2015 13:33:00 -0700
Subject: [PATCH] revlog: move delta check to it's own function

This moves the delta vs fulltext comparison to its own function. This will allow
us to reuse the function in future patches for more efficient delta choices. As
a side effect, this will also allow extensions to modify our delta criteria.
---
 mercurial/revlog.py | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/mercurial/revlog.py b/mercurial/revlog.py
index b202ab03ca..6c06c14d08 100644
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -1233,6 +1233,25 @@ class revlog(object):
             return ('u', text)
         return ("", bin)
 
+    def _isgooddelta(self, d, textlen):
+        """Returns True if the given delta is good. Good means that it is within
+        the disk span, disk size, and chain length bounds that we know to be
+        performant."""
+        if d is None:
+            return False
+
+        # - 'dist' is the distance from the base revision -- bounding it limits
+        #   the amount of I/O we need to do.
+        # - 'compresseddeltalen' is the sum of the total size of deltas we need
+        #   to apply -- bounding it limits the amount of CPU we consume.
+        dist, l, data, base, chainbase, chainlen, compresseddeltalen = d
+        if (dist > textlen * 4 or l > textlen or
+            compresseddeltalen > textlen * 2 or
+            (self._maxchainlen and chainlen > self._maxchainlen)):
+            return False
+
+        return True
+
     def _addrevision(self, node, text, transaction, link, p1, p2, flags,
                      cachedelta, ifh, dfh):
         """internal function to add revisions to the log
@@ -1334,13 +1353,7 @@ class revlog(object):
         else:
             textlen = len(text)
 
-        # - 'dist' is the distance from the base revision -- bounding it limits
-        #   the amount of I/O we need to do.
-        # - 'compresseddeltalen' is the sum of the total size of deltas we need
-        #   to apply -- bounding it limits the amount of CPU we consume.
-        if (d is None or dist > textlen * 4 or l > textlen or
-            compresseddeltalen > textlen * 2 or
-            (self._maxchainlen and chainlen > self._maxchainlen)):
+        if not self._isgooddelta(d, textlen):
             text = buildtext()
             data = self.compress(text)
             l = len(data[1]) + len(data[0])