[PATCH 3 of 4] revlog: make compress a method

[Bryan O'Sullivan]

# HG changeset patch
# User Bryan O'Sullivan <bryano at fb.com>
# Date 1340657773 25200
# Node ID e6054ad06d599fe5dca3172e9f9cd577208ff1b9
# Parent  e5a5191a08b8077e4d05e7bf32552cf382db07dd
revlog: make compress a method

This allows an extension to optionally use a new compression type based
on the options applied by the repo to the revlog's opener.

(decompress doesn't need the same treatment, as it can be replaced using
extensions.wrapfunction, and can figure out which compression algorithm
is in use based on the first byte of the compressed payload.)

diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -75,35 +75,6 @@ def hash(text, p1, p2):
     s.update(text)
     return s.digest()
 
-def compress(text):
-    """ generate a possibly-compressed representation of text """
-    if not text:
-        return ("", text)
-    l = len(text)
-    bin = None
-    if l < 44:
-        pass
-    elif l > 1000000:
-        # zlib makes an internal copy, thus doubling memory usage for
-        # large files, so lets do this in pieces
-        z = zlib.compressobj()
-        p = []
-        pos = 0
-        while pos < l:
-            pos2 = pos + 2**20
-            p.append(z.compress(text[pos:pos2]))
-            pos = pos2
-        p.append(z.flush())
-        if sum(map(len, p)) < l:
-            bin = "".join(p)
-    else:
-        bin = _compress(text)
-    if bin is None or len(bin) > l:
-        if text[0] == '\0':
-            return ("", text)
-        return ('u', text)
-    return ("", bin)
-
 def decompress(bin):
     """ decompress the given input """
     if not bin:
@@ -1008,6 +979,35 @@ class revlog(object):
                 dfh.close()
             ifh.close()
 
+    def compress(self, text):
+        """ generate a possibly-compressed representation of text """
+        if not text:
+            return ("", text)
+        l = len(text)
+        bin = None
+        if l < 44:
+            pass
+        elif l > 1000000:
+            # zlib makes an internal copy, thus doubling memory usage for
+            # large files, so lets do this in pieces
+            z = zlib.compressobj()
+            p = []
+            pos = 0
+            while pos < l:
+                pos2 = pos + 2**20
+                p.append(z.compress(text[pos:pos2]))
+                pos = pos2
+            p.append(z.flush())
+            if sum(map(len, p)) < l:
+                bin = "".join(p)
+        else:
+            bin = _compress(text)
+        if bin is None or len(bin) > l:
+            if text[0] == '\0':
+                return ("", text)
+            return ('u', text)
+        return ("", bin)
+
     def _addrevision(self, node, text, transaction, link, p1, p2,
                      cachedelta, ifh, dfh):
         """internal function to add revisions to the log
@@ -1040,7 +1040,7 @@ class revlog(object):
                 t = buildtext()
                 ptext = self.revision(self.node(rev))
                 delta = mdiff.textdiff(ptext, t)
-            data = compress(delta)
+            data = self.compress(delta)
             l = len(data[1]) + len(data[0])
             if basecache[0] == rev:
                 chainbase = basecache[1]
@@ -1084,7 +1084,7 @@ class revlog(object):
             textlen = len(text)
         if d is None or dist > textlen * 2:
             text = buildtext()
-            data = compress(text)
+            data = self.compress(text)
             l = len(data[1]) + len(data[0])
             base = chainbase = curr