[PATCH 4 of 4] obsstore: cache size computation for fm1 node

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1417073013 28800
#      Wed Nov 26 23:23:33 2014 -0800
# Node ID 3e522f212318e467c5919a74de52c85f1a3ee0e7
# Parent  0e7fa31502eeb5f3d347541e5c1caea4cb714d92
obsstore: cache size computation for fm1 node

We have two different types of node type (sha1 and sha256, only sha1 is used
now) and therefor different sizes for them. We now compute the value once
instead of redoing the computation every loop. This has no visible performance
impact.

diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -275,10 +275,12 @@ def _fm0decodemeta(data):
 # - remaining bytes: the metadata, each (key, value) pair after the other.
 _fm1version = 1
 _fm1fixed = '>IdhHBBB20s'
 _fm1nodesha1 = '20s'
 _fm1nodesha256 = '32s'
+_fm1nodesha1size = _calcsize(_fm1nodesha1)
+_fm1nodesha256size = _calcsize(_fm1nodesha256)
 _fm1fsize = _calcsize(_fm1fixed)
 _fm1parentnone = 3
 _fm1parentshift = 14
 _fm1parentmask = (_fm1parentnone << _fm1parentshift)
 _fm1metapair = 'BB'
@@ -297,13 +299,14 @@ def _fm1readmarkers(data, off=0):
         if numpar == _fm1parentnone:
             numpar = None
         # build the date tuple (upgrade tz minutes to seconds)
         date = (seconds, tz * 60)
         _fm1node = _fm1nodesha1
+        fnodesize = _fm1nodesha1size
         if flags & usingsha256:
             _fm1node = _fm1nodesha256
-        fnodesize = _calcsize(_fm1node)
+            fnodesize = _fm1nodesha256size
         # read replacement
         sucs = ()
         if numsuc:
             s = (fnodesize * numsuc)
             cur = data[off:off + s]