rbc: use struct unpack_from and pack_into instead of unpack and pack
These functions were introduced in Python 2.5 and are faster and simpler than
the old ones ... mainly because we can avoid intermediate buffers:
$ python -m timeit -s "_rbcrecfmt='>4sI'" -s 's = "x"*10000' -s 'from struct import unpack' 'unpack(_rbcrecfmt, buffer(s, 16, 8))'
1000000 loops, best of 3: 0.543 usec per loop
$ python -m timeit -s "_rbcrecfmt='>4sI'" -s 's = "x"*10000' -s 'from struct import unpack_from' 'unpack_from(_rbcrecfmt, s, 16)'
1000000 loops, best of 3: 0.323 usec per loop
$ python -m timeit -s "from array import array" -s "_rbcrecfmt='>4sI'" -s "s = array('c')" -s 's.fromstring("x"*10000)' -s 'from struct import pack' -s "rec = array('c')" 'rec.fromstring(pack(_rbcrecfmt, "asdf", 7))'
1000000 loops, best of 3: 0.364 usec per loop
$ python -m timeit -s "from array import array" -s "_rbcrecfmt='>4sI'" -s "s = array('c')" -s 's.fromstring("x"*10000)' -s 'from struct import pack_into' -s "rec = array('c')" -s 'rec.fromstring("x"*100)' 'pack_into(_rbcrecfmt, rec, 0, "asdf", 7)'
1000000 loops, best of 3: 0.229 usec per loop
--- a/mercurial/branchmap.py Sun Mar 12 15:27:02 2017 -0400
+++ b/mercurial/branchmap.py Wed Oct 19 02:46:35 2016 +0200
@@ -23,8 +23,8 @@
)
calcsize = struct.calcsize
-pack = struct.pack
-unpack = struct.unpack
+pack_into = struct.pack_into
+unpack_from = struct.unpack_from
def _filename(repo):
"""name of a branchcache file for a given repo or repoview"""
@@ -406,8 +406,7 @@
# fast path: extract data from cache, use it if node is matching
reponode = changelog.node(rev)[:_rbcnodelen]
- cachenode, branchidx = unpack(
- _rbcrecfmt, util.buffer(self._rbcrevs, rbcrevidx, _rbcrecsize))
+ cachenode, branchidx = unpack_from(_rbcrecfmt, self._rbcrevs, rbcrevidx)
close = bool(branchidx & _rbccloseflag)
if close:
branchidx &= _rbcbranchidxmask
@@ -451,12 +450,11 @@
def _setcachedata(self, rev, node, branchidx):
"""Writes the node's branch data to the in-memory cache data."""
rbcrevidx = rev * _rbcrecsize
- rec = bytearray(pack(_rbcrecfmt, node, branchidx))
if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
self._rbcrevs.extend('\0' *
(len(self._repo.changelog) * _rbcrecsize -
len(self._rbcrevs)))
- self._rbcrevs[rbcrevidx:rbcrevidx + _rbcrecsize] = rec
+ pack_into(_rbcrecfmt, self._rbcrevs, rbcrevidx, node, branchidx)
self._rbcrevslen = min(self._rbcrevslen, rev)
tr = self._repo.currenttransaction()