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bpo-27660: remove unnecessary overflow checks in list_resize (GH-189)

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Xiang Zhang 2017-02-22 12:32:30 +08:00 • committed by GitHub
parent 3e8d6cb189
commit 4cee049f5b
1 changed files with 7 additions and 12 deletions
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19
Objects/listobject.c
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@ -26,7 +26,7 @@ static int
list_resize(PyListObject *self, Py_ssize_t newsize) list_resize(PyListObject *self, Py_ssize_t newsize)
{ {
PyObject **items; PyObject **items;
size_t new_allocated; size_t new_allocated, num_allocated_bytes;
Py_ssize_t allocated = self->allocated; Py_ssize_t allocated = self->allocated;
/* Bypass realloc() when a previous overallocation is large enough /* Bypass realloc() when a previous overallocation is large enough
@ -45,24 +45,19 @@ list_resize(PyListObject *self, Py_ssize_t newsize)
* sequence of appends() in the presence of a poorly-performing * sequence of appends() in the presence of a poorly-performing
* system realloc(). * system realloc().
* The growth pattern is: 0, 4, 8, 16, 25, 35, 46, 58, 72, 88, ... * 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); new_allocated = (size_t)newsize + (newsize >> 3) + (newsize < 9 ? 3 : 6);
if (new_allocated > (size_t)PY_SSIZE_T_MAX / sizeof(PyObject *)) {
/* check for integer overflow */
if (new_allocated > SIZE_MAX - newsize) {
PyErr_NoMemory(); PyErr_NoMemory();
return -1; return -1;
} else {
new_allocated += newsize;
} }
if (newsize == 0) if (newsize == 0)
new_allocated = 0; new_allocated = 0;
items = self->ob_item; num_allocated_bytes = new_allocated * sizeof(PyObject *);
if (new_allocated <= (SIZE_MAX / sizeof(PyObject *))) items = (PyObject **)PyMem_Realloc(self->ob_item, num_allocated_bytes);
PyMem_RESIZE(items, PyObject *, new_allocated);
else
items = NULL;
if (items == NULL) { if (items == NULL) {
PyErr_NoMemory(); PyErr_NoMemory();
return -1; return -1;