filelog: add hash-based comparisons

For status, rather than reconstruct full file versions from revlog for
comparison, compare hashes.

mercurial/filelog.py

@@ -65,6 +65,27 b' class filelog(revlog):'
             return (m["copy"], bin(m["copyrev"]))
         return False
 
+    def cmp(self, node, text):
+        """compare text with a given file revision"""
+
+        # for renames, we have to go the slow way
+        if self.renamed(node):
+            t2 = self.read(node)
+            return t2 == text
+
+        p1, p2 = self.parents(node)
+        h = hash(text, p1, p2)
+
+        return h != node
+
+    def makenode(self, node, text):
+        """calculate a file nodeid for text, descended or possibly
+        unchanged from node"""
+
+        if self.cmp(node, text):
+            return hash(text, node, nullid)
+        return node
+
     def annotate(self, node):
 
         def decorate(text, rev):

mercurial/localrepo.py

@@ -668,8 +668,7 b' class localrepository(repo.repository):'
 
         def fcmp(fn, mf):
             t1 = self.wread(fn)
-            t2 = self.file(fn).read(mf.get(fn, nullid))
-            return cmp(t1, t2)
+            return self.file(fn).cmp(mf.get(fn, nullid), t1)
 
         def mfmatches(node):
             change = self.changelog.read(node)