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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
This commit is contained in:
Raymond Hettinger 2013-07-05 18:05:29 -10:00
parent 6597aa16b6
commit de68e0cf0e
2 changed files with 2 additions and 2 deletions
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2
Lib/test/test_deque.py
View File

@ -536,7 +536,7 @@ class TestBasic(unittest.TestCase):
@support.cpython_only @support.cpython_only
def test_sizeof(self): def test_sizeof(self):
BLOCKLEN = 62 BLOCKLEN = 64
basesize = support.calcobjsize('2P4nlP') basesize = support.calcobjsize('2P4nlP')
blocksize = struct.calcsize('2P%dP' % BLOCKLEN) blocksize = struct.calcsize('2P%dP' % BLOCKLEN)
self.assertEqual(object.__sizeof__(deque()), basesize) self.assertEqual(object.__sizeof__(deque()), basesize)

2
Modules/_collectionsmodule.c
View File

@ -14,7 +14,7 @@
* division/modulo computations during indexing. * division/modulo computations during indexing.
*/ */
#define BLOCKLEN 62 #define BLOCKLEN 64
#define CENTER ((BLOCKLEN - 1) / 2) #define CENTER ((BLOCKLEN - 1) / 2)
/* A `dequeobject` is composed of a doubly-linked list of `block` nodes. /* A `dequeobject` is composed of a doubly-linked list of `block` nodes.