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bpo-27660: remove unnecessary overflow checks in list_resize by zhangyangyu · Pull Request #189 · python/cpython · GitHub
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bpo-27660: remove unnecessary overflow checks in list_resize #189

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zhangyangyu merged 2 commits into from
Feb 22, 2017
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bpo-27660: remove unnecessary overflow checks in list_resize #189

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35d79fa
bpo-27660: remove unnecessary overflow checks in list_resize
zhangyangyu Feb 20, 2017
529f333
fix two style nits by Raymond
zhangyangyu Feb 21, 2017
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fix two style nits by Raymond
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@zhangyangyu
zhangyangyu committed Feb 21, 2017
commit 529f3333a41a4083fb8894044f61e8dc865bee17
12 changes: 6 additions & 6 deletions Objects/listobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ static int
list_resize(PyListObject *self, Py_ssize_t newsize)
{
PyObject **items;
size_t new_allocated, size;
size_t new_allocated, num_allocated_bytes;
Py_ssize_t allocated = self->allocated;

/* Bypass realloc() when a previous overallocation is large enough
Expand All @@ -45,19 +45,19 @@ list_resize(PyListObject *self, Py_ssize_t newsize)
* sequence of appends() in the presence of a poorly-performing
* system realloc().
* The growth pattern is: 0, 4, 8, 16, 25, 35, 46, 58, 72, 88, ...
* Note: new_allocated won't overflow because the largest possible value
* is PY_SSIZE_T_MAX * (9 / 8) + 6 which always fits in a size_t.
*/
new_allocated = (newsize >> 3) + (newsize < 9 ? 3 : 6);
/* can't overflow, largest number is PY_SSIZE_T_MAX * (9 / 8) + 6 */
new_allocated += (size_t)newsize;
new_allocated = (size_t)newsize + (newsize >> 3) + (newsize < 9 ? 3 : 6);
if (new_allocated > (size_t)PY_SSIZE_T_MAX / sizeof(PyObject *)) {
PyErr_NoMemory();
return -1;
}

if (newsize == 0)
new_allocated = 0;
size = new_allocated * sizeof(PyObject *);
items = (PyObject **)PyMem_Realloc(self->ob_item, size);
num_allocated_bytes = new_allocated * sizeof(PyObject *);
items = (PyObject **)PyMem_Realloc(self->ob_item, num_allocated_bytes);
if (items == NULL) {
PyErr_NoMemory();
return -1;
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