Correct handling of overflowed or infinite sums

python · Dec 23, 2022 · 4f4b731 · 4f4b731
1 parent af7613e
commit 4f4b731
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Showing 2 changed files with 7 additions and 1 deletion.
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
@@ -9,6 +9,7 @@
 import gc
 import io
 import locale
+import math
 import os
 import pickle
 import platform
@@ -1624,6 +1625,8 @@ def test_sum(self):
         self.assertEqual(repr(sum([-0.0])), '0.0')
         self.assertEqual(repr(sum([-0.0], -0.0)), '-0.0')
         self.assertEqual(repr(sum([], -0.0)), '-0.0')
+        self.assertTrue(math.isinf(sum([float("inf"), float("inf")])))
+        self.assertTrue(math.isinf(sum([1e308, 1e308])))
 
         self.assertRaises(TypeError, sum)
         self.assertRaises(TypeError, sum, 42)

diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
@@ -2541,7 +2541,10 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
                 Py_DECREF(iter);
                 if (PyErr_Occurred())
                     return NULL;
-                if (c) {
+                /* Avoid losing the sign on a negative result,
+                   and don't let adding the compensation convert
+                   an infinite or overflowed sum to a NaN. */
+                if (c && Py_IS_FINITE(c)) {
                     f_result += c;
                 }
                 return PyFloat_FromDouble(f_result);