Only use lazy indexing for big indices and avoid the overhead of the

Only use lazy indexing for big indices and avoid the overhead of the
lazy index in the small index case.

--- a/mercurial/revlog.py	Fri May 20 17:34:04 2005 -0800
+++ b/mercurial/revlog.py	Fri May 20 17:35:20 2005 -0800
@@ -124,14 +124,34 @@
         self.datafile = datafile
         self.opener = opener
         self.cache = None
-        # read the whole index for now, handle on-demand later
+
         try:
             i = self.opener(self.indexfile).read()
         except IOError:
             i = ""
-        parser = lazyparser(i)
-        self.index = lazyindex(parser)
-        self.nodemap = lazymap(parser)
+
+        if len(i) > 10000:
+            # big index, let's parse it on demand
+            parser = lazyparser(i)
+            self.index = lazyindex(parser)
+            self.nodemap = lazymap(parser)
+        else:
+            s = struct.calcsize(indexformat)
+            l = len(i) / s
+            self.index = [None] * l
+            m = [None] * l
+
+            n = 0
+            for f in xrange(0, len(i), s):
+                # offset, size, base, linkrev, p1, p2, nodeid
+                e = struct.unpack(indexformat, i[f:f + s])
+                m[n] = (e[6], n)
+                self.index[n] = e
+                n += 1
+
+            self.nodemap = dict(m)
+            self.nodemap[nullid] = -1
+            
 
     def tip(self): return self.node(len(self.index) - 1)
     def count(self): return len(self.index)