Reduce string duplication in compression code

Reduce string duplication in compression code

This cuts down on string copies and allows buffers (instead of strings)
to be passed into the compression code

--- a/mercurial/revlog.py	Fri Nov 11 15:34:17 2005 -0800
+++ b/mercurial/revlog.py	Fri Nov 11 18:20:19 2005 -0800
@@ -31,15 +31,15 @@
 
 def compress(text):
     """ generate a possibly-compressed representation of text """
-    if not text: return text
+    if not text: return ("", text)
     if len(text) < 44:
-        if text[0] == '\0': return text
-        return 'u' + text
+        if text[0] == '\0': return ("", text)
+        return ('u', text)
     bin = zlib.compress(text)
     if len(bin) > len(text):
-        if text[0] == '\0': return text
-        return 'u' + text
-    return bin
+        if text[0] == '\0': return ("", text)
+        return ('u', text)
+    return ("", bin)
 
 def decompress(bin):
     """ decompress the given input """
@@ -543,14 +543,16 @@
             end = self.end(t)
             if not d:
                 prev = self.revision(self.tip())
-                d = self.diff(prev, text)
+                d = self.diff(prev, str(text))
             data = compress(d)
-            dist = end - start + len(data)
+            l = len(data[1]) + len(data[0])
+            dist = end - start + l
 
         # full versions are inserted when the needed deltas
         # become comparable to the uncompressed text
         if not n or dist > len(text) * 2:
             data = compress(text)
+            l = len(data[1]) + len(data[0])
             base = n
         else:
             base = self.base(t)
@@ -559,14 +561,17 @@
         if t >= 0:
             offset = self.end(t)
 
-        e = (offset, len(data), base, link, p1, p2, node)
+        e = (offset, l, base, link, p1, p2, node)
 
         self.index.append(e)
         self.nodemap[node] = n
         entry = struct.pack(indexformat, *e)
 
         transaction.add(self.datafile, e[0])
-        self.opener(self.datafile, "a").write(data)
+        f = self.opener(self.datafile, "a")
+        if data[0]:
+            f.write(data[0])
+        f.write(data[1])
         transaction.add(self.indexfile, n * len(entry))
         self.opener(self.indexfile, "a").write(entry)
 
@@ -801,7 +806,8 @@
             # current size.
 
             if chain == prev:
-                cdelta = compress(delta)
+                tempd = compress(delta)
+                cdelta = tempd[0] + tempd[1]
 
             if chain != prev or (end - start + len(cdelta)) > measure * 2:
                 # flush our writes here so we can read it in revision