From: Ross Lagerwall <rosslagerwall@gmail.com>
Date: Thu, 17 May 2012 17:49:27 +0000 (+0200)
Subject: Issue #13031: Small speed-up for tarfile when unzipping tarfiles.
X-Git-Tag: v3.3.0a4~140^2
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=468ff4c3ed07b815898a749eca14e9ae1ea76893;p=python

Issue #13031: Small speed-up for tarfile when unzipping tarfiles.
Patch by Justin Peel.
---

diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 9d38421ef6..854967751d 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -245,8 +245,8 @@ def calc_chksums(buf):
        the high bit set. So we calculate two checksums, unsigned and
        signed.
     """
-    unsigned_chksum = 256 + sum(struct.unpack("148B", buf[:148]) + struct.unpack("356B", buf[156:512]))
-    signed_chksum = 256 + sum(struct.unpack("148b", buf[:148]) + struct.unpack("356b", buf[156:512]))
+    unsigned_chksum = 256 + sum(struct.unpack_from("148B8x356B", buf))
+    signed_chksum = 256 + sum(struct.unpack_from("148b8x356b", buf))
     return unsigned_chksum, signed_chksum
 
 def copyfileobj(src, dst, length=None):
diff --git a/Misc/ACKS b/Misc/ACKS
index b9750b92ae..fc65795c7a 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -776,6 +776,7 @@ Gaël Pasgrimaud
 Joe Peterson
 Randy Pausch
 Samuele Pedroni
+Justin Peel
 Marcel van der Peijl
 Berker Peksag
 Steven Pemberton
diff --git a/Misc/NEWS b/Misc/NEWS
index 456f256a2a..c83d3d36ab 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -38,6 +38,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #13031: Small speed-up for tarfile when unzipping tarfiles.
+  Patch by Justin Peel.
+
 - Issue #14780: urllib.request.urlopen() now has a ``cadefault`` argument
   to use the default certificate store.  Initial patch by James Oakley.