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Issue #28731: Optimize _PyDict_NewPresized() to create correct size dict.

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Improve speed of dict literal with constant keys up to 30%.
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INADA Naoki 2016-12-07 18:34:44 +09:00
parent 0c78634d78
commit 2c5a830f2a
2 changed files with 22 additions and 5 deletions
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3
Misc/NEWS
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@ -10,6 +10,9 @@ What's New in Python 3.6.1 release candidate 1
Core and Builtins Core and Builtins
----------------- -----------------
- Issue #28731: Optimize _PyDict_NewPresized() to create correct size dict.
Improve speed of dict literal with constant keys up to 30%.
- Issue #5322: Fixed setting __new__ to a PyCFunction inside Python code. - Issue #5322: Fixed setting __new__ to a PyCFunction inside Python code.
Original patch by Andreas Stührk. Original patch by Andreas Stührk.

24
Objects/dictobject.c
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@ -388,7 +388,7 @@ dk_set_index(PyDictKeysObject *keys, Py_ssize_t i, Py_ssize_t ix)
* This can be used to reserve enough size to insert n entries without * This can be used to reserve enough size to insert n entries without
* resizing. * resizing.
*/ */
#define ESTIMATE_SIZE(n) (((n)*3) >> 1) #define ESTIMATE_SIZE(n) (((n)*3+1) >> 1)
/* Alternative fraction that is otherwise close enough to 2n/3 to make /* Alternative fraction that is otherwise close enough to 2n/3 to make
* little difference. 8 * 2/3 == 8 * 5/8 == 5. 16 * 2/3 == 16 * 5/8 == 10. * little difference. 8 * 2/3 == 8 * 5/8 == 5. 16 * 2/3 == 16 * 5/8 == 10.
@ -1357,12 +1357,26 @@ make_keys_shared(PyObject *op)
PyObject * PyObject *
_PyDict_NewPresized(Py_ssize_t minused) _PyDict_NewPresized(Py_ssize_t minused)
{ {
const Py_ssize_t max_presize = 128 * 1024;
Py_ssize_t newsize; Py_ssize_t newsize;
PyDictKeysObject *new_keys; PyDictKeysObject *new_keys;
for (newsize = PyDict_MINSIZE;
newsize <= minused && newsize > 0; /* There are no strict guarantee that returned dict can contain minused
newsize <<= 1) * items without resize. So we create medium size dict instead of very
; * large dict or MemoryError.
*/
if (minused > USABLE_FRACTION(max_presize)) {
newsize = max_presize;
}
else {
Py_ssize_t minsize = ESTIMATE_SIZE(minused);
newsize = PyDict_MINSIZE;
while (newsize < minsize) {
newsize <<= 1;
}
}
assert(IS_POWER_OF_2(newsize));
new_keys = new_keys_object(newsize); new_keys = new_keys_object(newsize);
if (new_keys == NULL) if (new_keys == NULL)
return NULL; return NULL;