From 227f0faed2138cebd43cf1973d8bb72ad70fca5a Mon Sep 17 00:00:00 2001 From: Benjamin Peterson Date: Tue, 25 Jun 2013 11:34:48 -0700 Subject: reapply 5accb0ac8bfb --- Lib/test/test_deque.py | 2 +- Modules/_collectionsmodule.c | 18 +++++++----------- 2 files changed, 8 insertions(+), 12 deletions(-) diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py index 595a0c4..98b203e 100644 --- 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 + BLOCKLEN = 64 basesize = test_support.calcobjsize('2P4PlP') blocksize = struct.calcsize('2P%dP' % BLOCKLEN) self.assertEqual(object.__sizeof__(deque()), basesize) diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c index 371631c..8a43d9a 100644 --- 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 - * close. There is some extra margin to prevent spurious arithmetic - * overflows at various places. The following check ensures that - * the blocks allocated to the deque, in the worst case, can only - * have PY_SSIZE_T_MAX-2 entries in total. - */ + /* 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. */ if (len >= PY_SSIZE_T_MAX - 2*BLOCKLEN) { PyErr_SetString(PyExc_OverflowError, "cannot add more blocks to the deque"); -- cgit v0.12