diff options
Diffstat (limited to 'Modules/_collectionsmodule.c')
| -rw-r--r-- | Modules/_collectionsmodule.c | 18 |
1 files changed, 7 insertions, 11 deletions
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"); |