--- a/util.py
+++ b/util.py
@@ -1,6 +1,9 @@
 import os
+import pickle
 import shutil
 
+from mercurial import node
+
 svn_subcommands = { }
 
 def register_subcommand(name):
@@ -18,3 +21,37 @@ def wipe_all_files(hg_wc_path):
             shutil.rmtree(f)
         else:
             os.remove(f)
+
+REVMAP_FILE_VERSION = 1
+def parse_revmap(revmap_filename):
+    revmap = {}
+    f = open(revmap_filename)
+    try:
+        # Remove compat code after March of 2009. That should be more than long
+        # enough.
+        revmap = pickle.load(f)
+        f.close()
+        f = open(revmap_filename, 'w')
+        f.write('1\n')
+        for key, value in sorted(revmap.items()):
+            f.write('%s %s %s\n' % (str(key[0]), node.hex(value), key[1] or ''))
+        f.close()
+    except:
+        f.close()
+        f = open(revmap_filename)
+        ver = int(f.readline())
+        if ver == 1:
+            for l in f:
+                revnum, node_hash, branch = l.split(' ', 2)
+                if branch == '\n':
+                    branch = None
+                else:
+                    branch = branch[:-1]
+                revmap[int(revnum), branch] = node.bin(node_hash)
+            f.close()
+        else:
+            print ('Your revmap was made by a newer version of hgsubversion.'
+                   ' Please upgrade.')
+            raise NotImplementedError
+    return revmap
+