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gh-92914: Round the allocated size for lists up to the even number #92915

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Merged
serhiy-storchaka merged 5 commits into from
May 19, 2022
Merged

gh-92914: Round the allocated size for lists up to the even number #92915

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9a2ed09
gh-92914: Always round up the size allocated for lists up to 16 bytes
serhiy-storchaka May 18, 2022
a6b1a79
Round up to the even number.
serhiy-storchaka May 18, 2022
8599f81
Fix tests.
serhiy-storchaka May 18, 2022
67779ed
Update 2022-05-18-08-32-33.gh-issue-92914.tJUeTD.rst
serhiy-storchaka May 18, 2022
7025f22
Update 2022-05-18-08-32-33.gh-issue-92914.tJUeTD.rst
serhiy-storchaka May 18, 2022
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Round up to the even number.
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@serhiy-storchaka
serhiy-storchaka committed May 18, 2022
commit a6b1a798e67795a001bff775f8c71b7d9d5f98a1
14 changes: 5 additions & 9 deletions Objects/listobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -94,16 +94,12 @@ list_preallocate_exact(PyListObject *self, Py_ssize_t size)
assert(self->ob_item == NULL);
assert(size > 0);

/* Since the Python memory allocator has granularity of 16 bytes,
* there is no benefit of allocating space for the odd number of items,
* and there is no drawback of rounding it up.
/* Since the Python memory allocator has granularity of 16 bytes on 64-bit
* platforms (8 on 32-bit), there is no benefit of allocating space for
* the odd number of items, and there is no drawback of rounding the
* allocated size up to the nearest even number.
*/
if (sizeof(PyObject*) > 4) {
size = (size + 1) & ~(size_t)1;
}
else {
size = (size + 3) & ~(size_t)3;
}
size = (size + 1) & ~(size_t)1;
PyObject **items = PyMem_New(PyObject*, size);
if (items == NULL) {
PyErr_NoMemory();
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