From: Raymond Hettinger <python@rcn.com>
Date: Sat, 6 Jul 2013 04:05:29 +0000 (-1000)
Subject: Speed-up deque indexing by changing the deque block length to a power of two.
X-Git-Tag: v3.4.0a1~326
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=de68e0cf0e6d94b087a3b7ae40e50843dff6d918;p=python

Speed-up deque indexing by changing the deque block length to a power of two.

The division and modulo calculation in deque_item() can be compiled
to fast bitwise operations when the BLOCKLEN is a power of two.

Timing before:

 ~/cpython $ py -m timeit -r7 -s 'from collections import deque' -s 'd=deque(range(10))' 'd[5]'
10000000 loops, best of 7: 0.0627 usec per loop

Timing after:

~/cpython $ py -m timeit -r7 -s 'from collections import deque' -s 'd=deque(range(10))' 'd[5]'
10000000 loops, best of 7: 0.0581 usec per loop
---

diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index a8487d2d95..e782b99203 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -536,7 +536,7 @@ class TestBasic(unittest.TestCase):
 
     @support.cpython_only
     def test_sizeof(self):
-        BLOCKLEN = 62
+        BLOCKLEN = 64
         basesize = support.calcobjsize('2P4nlP')
         blocksize = struct.calcsize('2P%dP' % BLOCKLEN)
         self.assertEqual(object.__sizeof__(deque()), basesize)
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index b9224754db..781949d48f 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -14,7 +14,7 @@
  * division/modulo computations during indexing.
  */
 
-#define BLOCKLEN 62
+#define BLOCKLEN 64
 #define CENTER ((BLOCKLEN - 1) / 2)
 
 /* A `dequeobject` is composed of a doubly-linked list of `block` nodes.