cpython: 5accb0ac8bfb (original) (raw)

Mercurial > cpython

changeset 84116:5accb0ac8bfb 2.7

Fix comment blocks. Adjust blocksize to a power-of-two for better divmod computations.

Raymond Hettinger python@rcn.com
date	Fri, 14 Jun 2013 01:06:33 -0400
parents	ca8e86711403
children	aff0bdab358e
files	Lib/test/test_deque.py Modules/_collectionsmodule.c
diffstat	2 files changed, 8 insertions(+), 12 deletions(-)[+] [-] Lib/test/test_deque.py 2 Modules/_collectionsmodule.c 18

line wrap: on

line diff

--- a/Lib/test/test_deque.py +++ b/Lib/test/test_deque.py @@ -522,7 +522,7 @@ class TestBasic(unittest.TestCase): @test_support.cpython_only def test_sizeof(self):

```
   BLOCKLEN = 62[](#l1.7)
```

   BLOCKLEN = 64[](#l1.8)
   basesize = test_support.calcobjsize('2P4PlP')[](#l1.9)
   blocksize = struct.calcsize('2P%dP' % BLOCKLEN)[](#l1.10)
   self.assertEqual(object.__sizeof__(deque()), basesize)[](#l1.11)

--- a/Modules/_collectionsmodule.c +++ b/Modules/_collectionsmodule.c @@ -8,12 +8,13 @@ / / The block length may be set to any number over 1. Larger numbers

- reduce the number of calls to the memory allocator but take more
- memory. Ideally, BLOCKLEN should be set with an eye to the
- length of a cache line.

- reduce the number of calls to the memory allocator, give faster
- indexing and rotation, and reduce the link::data overhead ratio.
- Ideally, the block length should be a power-of-two for faster
- 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. @@ -58,13 +59,8 @@ static block *freeblocks[MAXFREEBLOCKS]; static block * newblock(block *leftlink, block *rightlink, Py_ssize_t len) { block *b;

/* To prevent len from overflowing PY_SSIZE_T_MAX on 64-bit machines, we

* refuse to allocate new blocks if the current len is dangerously[](#l2.26)

* close.  There is some extra margin to prevent spurious arithmetic[](#l2.27)

* overflows at various places.  The following check ensures that[](#l2.28)

* the blocks allocated to the deque, in the worst case, can only[](#l2.29)

* have PY_SSIZE_T_MAX-2 entries in total.[](#l2.30)

```
*/[](#l2.31)
```

/* To prevent len from overflowing PY_SSIZE_T_MAX on 32-bit machines, we
```
* refuse to allocate new blocks if the current len is nearing overflow. */[](#l2.33)
```
if (len >= PY_SSIZE_T_MAX - 2*BLOCKLEN) { PyErr_SetString(PyExc_OverflowError, "cannot add more blocks to the deque");